blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
/*
* buffered writeback throttling . loosely based on CoDel . We can ' t drop
* packets for IO scheduling , so the logic is something like this :
*
* - Monitor latencies in a defined window of time .
* - If the minimum latency in the above window exceeds some target , increment
* scaling step and scale down queue depth by a factor of 2 x . The monitoring
* window is then shrunk to 100 / sqrt ( scaling step + 1 ) .
* - For any window where we don ' t have solid data on what the latencies
* look like , retain status quo .
* - If latencies look good , decrement scaling step .
* - If we ' re only doing writes , allow the scaling step to go negative . This
* will temporarily boost write performance , snapping back to a stable
* scaling step of 0 if reads show up or the heavy writers finish . Unlike
* positive scaling steps where we shrink the monitoring window , a negative
* scaling step retains the default step = = 0 window size .
*
* Copyright ( C ) 2016 Jens Axboe
*
*/
# include <linux/kernel.h>
# include <linux/blk_types.h>
# include <linux/slab.h>
# include <linux/backing-dev.h>
# include <linux/swap.h>
# include "blk-wbt.h"
2018-07-03 18:32:35 +03:00
# include "blk-rq-qos.h"
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
# define CREATE_TRACE_POINTS
# include <trace/events/wbt.h>
2018-05-09 12:08:48 +03:00
static inline void wbt_clear_state ( struct request * rq )
2018-05-09 12:08:47 +03:00
{
2018-05-09 12:08:50 +03:00
rq - > wbt_flags = 0 ;
2018-05-09 12:08:47 +03:00
}
2018-05-09 12:08:48 +03:00
static inline enum wbt_flags wbt_flags ( struct request * rq )
2018-05-09 12:08:47 +03:00
{
2018-05-09 12:08:50 +03:00
return rq - > wbt_flags ;
2018-05-09 12:08:47 +03:00
}
2018-05-09 12:08:48 +03:00
static inline bool wbt_is_tracked ( struct request * rq )
2018-05-09 12:08:47 +03:00
{
2018-05-09 12:08:50 +03:00
return rq - > wbt_flags & WBT_TRACKED ;
2018-05-09 12:08:47 +03:00
}
2018-05-09 12:08:48 +03:00
static inline bool wbt_is_read ( struct request * rq )
2018-05-09 12:08:47 +03:00
{
2018-05-09 12:08:50 +03:00
return rq - > wbt_flags & WBT_READ ;
2018-05-09 12:08:47 +03:00
}
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
enum {
/*
* Default setting , we ' ll scale up ( to 75 % of QD max ) or down ( min 1 )
* from here depending on device stats
*/
RWB_DEF_DEPTH = 16 ,
/*
* 100 msec window
*/
RWB_WINDOW_NSEC = 100 * 1000 * 1000ULL ,
/*
* Disregard stats , if we don ' t meet this minimum
*/
RWB_MIN_WRITE_SAMPLES = 3 ,
/*
* If we have this number of consecutive windows with not enough
* information to scale up or down , scale up .
*/
RWB_UNKNOWN_BUMP = 5 ,
} ;
static inline bool rwb_enabled ( struct rq_wb * rwb )
{
return rwb & & rwb - > wb_normal ! = 0 ;
}
static void wb_timestamp ( struct rq_wb * rwb , unsigned long * var )
{
if ( rwb_enabled ( rwb ) ) {
const unsigned long cur = jiffies ;
if ( cur ! = * var )
* var = cur ;
}
}
/*
* If a task was rate throttled in balance_dirty_pages ( ) within the last
* second or so , use that to indicate a higher cleaning rate .
*/
static bool wb_recent_wait ( struct rq_wb * rwb )
{
2018-07-03 18:32:35 +03:00
struct bdi_writeback * wb = & rwb - > rqos . q - > backing_dev_info - > wb ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
return time_before ( jiffies , wb - > dirty_sleep + HZ ) ;
}
2018-05-07 18:57:08 +03:00
static inline struct rq_wait * get_rq_wait ( struct rq_wb * rwb ,
enum wbt_flags wb_acct )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
2018-05-07 18:57:08 +03:00
if ( wb_acct & WBT_KSWAPD )
return & rwb - > rq_wait [ WBT_RWQ_KSWAPD ] ;
2018-05-07 19:03:23 +03:00
else if ( wb_acct & WBT_DISCARD )
return & rwb - > rq_wait [ WBT_RWQ_DISCARD ] ;
2018-05-07 18:57:08 +03:00
return & rwb - > rq_wait [ WBT_RWQ_BG ] ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
static void rwb_wake_all ( struct rq_wb * rwb )
{
int i ;
for ( i = 0 ; i < WBT_NUM_RWQ ; i + + ) {
struct rq_wait * rqw = & rwb - > rq_wait [ i ] ;
2018-08-20 22:20:50 +03:00
if ( wq_has_sleeper ( & rqw - > wait ) )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
wake_up_all ( & rqw - > wait ) ;
}
}
2018-07-03 18:32:35 +03:00
static void __wbt_done ( struct rq_qos * rqos , enum wbt_flags wb_acct )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
2018-07-03 18:32:35 +03:00
struct rq_wb * rwb = RQWB ( rqos ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
struct rq_wait * rqw ;
int inflight , limit ;
if ( ! ( wb_acct & WBT_TRACKED ) )
return ;
2018-05-07 18:57:08 +03:00
rqw = get_rq_wait ( rwb , wb_acct ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
inflight = atomic_dec_return ( & rqw - > inflight ) ;
/*
* wbt got disabled with IO in flight . Wake up any potential
* waiters , we don ' t have to do more than that .
*/
if ( unlikely ( ! rwb_enabled ( rwb ) ) ) {
rwb_wake_all ( rwb ) ;
return ;
}
/*
2018-05-07 19:03:23 +03:00
* For discards , our limit is always the background . For writes , if
* the device does write back caching , drop further down before we
* wake people up .
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
*/
2018-05-07 19:03:23 +03:00
if ( wb_acct & WBT_DISCARD )
limit = rwb - > wb_background ;
else if ( rwb - > wc & & ! wb_recent_wait ( rwb ) )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
limit = 0 ;
else
limit = rwb - > wb_normal ;
/*
* Don ' t wake anyone up if we are above the normal limit .
*/
if ( inflight & & inflight > = limit )
return ;
2018-08-20 22:20:50 +03:00
if ( wq_has_sleeper ( & rqw - > wait ) ) {
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
int diff = limit - inflight ;
if ( ! inflight | | diff > = rwb - > wb_background / 2 )
blk-wbt: Avoid lock contention and thundering herd issue in wbt_wait
I am currently running a large bare metal instance (i3.metal)
on EC2 with 72 cores, 512GB of RAM and NVME drives, with a
4.18 kernel. I have a workload that simulates a database
workload and I am running into lockup issues when writeback
throttling is enabled,with the hung task detector also
kicking in.
Crash dumps show that most CPUs (up to 50 of them) are
all trying to get the wbt wait queue lock while trying to add
themselves to it in __wbt_wait (see stack traces below).
[ 0.948118] CPU: 45 PID: 0 Comm: swapper/45 Not tainted 4.14.51-62.38.amzn1.x86_64 #1
[ 0.948119] Hardware name: Amazon EC2 i3.metal/Not Specified, BIOS 1.0 10/16/2017
[ 0.948120] task: ffff883f7878c000 task.stack: ffffc9000c69c000
[ 0.948124] RIP: 0010:native_queued_spin_lock_slowpath+0xf8/0x1a0
[ 0.948125] RSP: 0018:ffff883f7fcc3dc8 EFLAGS: 00000046
[ 0.948126] RAX: 0000000000000000 RBX: ffff887f7709ca68 RCX: ffff883f7fce2a00
[ 0.948128] RDX: 000000000000001c RSI: 0000000000740001 RDI: ffff887f7709ca68
[ 0.948129] RBP: 0000000000000002 R08: 0000000000b80000 R09: 0000000000000000
[ 0.948130] R10: ffff883f7fcc3d78 R11: 000000000de27121 R12: 0000000000000002
[ 0.948131] R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000
[ 0.948132] FS: 0000000000000000(0000) GS:ffff883f7fcc0000(0000) knlGS:0000000000000000
[ 0.948134] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.948135] CR2: 000000c424c77000 CR3: 0000000002010005 CR4: 00000000003606e0
[ 0.948136] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.948137] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.948138] Call Trace:
[ 0.948139] <IRQ>
[ 0.948142] do_raw_spin_lock+0xad/0xc0
[ 0.948145] _raw_spin_lock_irqsave+0x44/0x4b
[ 0.948149] ? __wake_up_common_lock+0x53/0x90
[ 0.948150] __wake_up_common_lock+0x53/0x90
[ 0.948155] wbt_done+0x7b/0xa0
[ 0.948158] blk_mq_free_request+0xb7/0x110
[ 0.948161] __blk_mq_complete_request+0xcb/0x140
[ 0.948166] nvme_process_cq+0xce/0x1a0 [nvme]
[ 0.948169] nvme_irq+0x23/0x50 [nvme]
[ 0.948173] __handle_irq_event_percpu+0x46/0x300
[ 0.948176] handle_irq_event_percpu+0x20/0x50
[ 0.948179] handle_irq_event+0x34/0x60
[ 0.948181] handle_edge_irq+0x77/0x190
[ 0.948185] handle_irq+0xaf/0x120
[ 0.948188] do_IRQ+0x53/0x110
[ 0.948191] common_interrupt+0x87/0x87
[ 0.948192] </IRQ>
....
[ 0.311136] CPU: 4 PID: 9737 Comm: run_linux_amd64 Not tainted 4.14.51-62.38.amzn1.x86_64 #1
[ 0.311137] Hardware name: Amazon EC2 i3.metal/Not Specified, BIOS 1.0 10/16/2017
[ 0.311138] task: ffff883f6e6a8000 task.stack: ffffc9000f1ec000
[ 0.311141] RIP: 0010:native_queued_spin_lock_slowpath+0xf5/0x1a0
[ 0.311142] RSP: 0018:ffffc9000f1efa28 EFLAGS: 00000046
[ 0.311144] RAX: 0000000000000000 RBX: ffff887f7709ca68 RCX: ffff883f7f722a00
[ 0.311145] RDX: 0000000000000035 RSI: 0000000000d80001 RDI: ffff887f7709ca68
[ 0.311146] RBP: 0000000000000202 R08: 0000000000140000 R09: 0000000000000000
[ 0.311147] R10: ffffc9000f1ef9d8 R11: 000000001a249fa0 R12: ffff887f7709ca68
[ 0.311148] R13: ffffc9000f1efad0 R14: 0000000000000000 R15: ffff887f7709ca00
[ 0.311149] FS: 000000c423f30090(0000) GS:ffff883f7f700000(0000) knlGS:0000000000000000
[ 0.311150] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.311151] CR2: 00007feefcea4000 CR3: 0000007f7016e001 CR4: 00000000003606e0
[ 0.311152] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.311153] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.311154] Call Trace:
[ 0.311157] do_raw_spin_lock+0xad/0xc0
[ 0.311160] _raw_spin_lock_irqsave+0x44/0x4b
[ 0.311162] ? prepare_to_wait_exclusive+0x28/0xb0
[ 0.311164] prepare_to_wait_exclusive+0x28/0xb0
[ 0.311167] wbt_wait+0x127/0x330
[ 0.311169] ? finish_wait+0x80/0x80
[ 0.311172] ? generic_make_request+0xda/0x3b0
[ 0.311174] blk_mq_make_request+0xd6/0x7b0
[ 0.311176] ? blk_queue_enter+0x24/0x260
[ 0.311178] ? generic_make_request+0xda/0x3b0
[ 0.311181] generic_make_request+0x10c/0x3b0
[ 0.311183] ? submit_bio+0x5c/0x110
[ 0.311185] submit_bio+0x5c/0x110
[ 0.311197] ? __ext4_journal_stop+0x36/0xa0 [ext4]
[ 0.311210] ext4_io_submit+0x48/0x60 [ext4]
[ 0.311222] ext4_writepages+0x810/0x11f0 [ext4]
[ 0.311229] ? do_writepages+0x3c/0xd0
[ 0.311239] ? ext4_mark_inode_dirty+0x260/0x260 [ext4]
[ 0.311240] do_writepages+0x3c/0xd0
[ 0.311243] ? _raw_spin_unlock+0x24/0x30
[ 0.311245] ? wbc_attach_and_unlock_inode+0x165/0x280
[ 0.311248] ? __filemap_fdatawrite_range+0xa3/0xe0
[ 0.311250] __filemap_fdatawrite_range+0xa3/0xe0
[ 0.311253] file_write_and_wait_range+0x34/0x90
[ 0.311264] ext4_sync_file+0x151/0x500 [ext4]
[ 0.311267] do_fsync+0x38/0x60
[ 0.311270] SyS_fsync+0xc/0x10
[ 0.311272] do_syscall_64+0x6f/0x170
[ 0.311274] entry_SYSCALL_64_after_hwframe+0x42/0xb7
In the original patch, wbt_done is waking up all the exclusive
processes in the wait queue, which can cause a thundering herd
if there is a large number of writer threads in the queue. The
original intention of the code seems to be to wake up one thread
only however, it uses wake_up_all() in __wbt_done(), and then
uses the following check in __wbt_wait to have only one thread
actually get out of the wait loop:
if (waitqueue_active(&rqw->wait) &&
rqw->wait.head.next != &wait->entry)
return false;
The problem with this is that the wait entry in wbt_wait is
define with DEFINE_WAIT, which uses the autoremove wakeup function.
That means that the above check is invalid - the wait entry will
have been removed from the queue already by the time we hit the
check in the loop.
Secondly, auto-removing the wait entries also means that the wait
queue essentially gets reordered "randomly" (e.g. threads re-add
themselves in the order they got to run after being woken up).
Additionally, new requests entering wbt_wait might overtake requests
that were queued earlier, because the wait queue will be
(temporarily) empty after the wake_up_all, so the waitqueue_active
check will not stop them. This can cause certain threads to starve
under high load.
The fix is to leave the woken up requests in the queue and remove
them in finish_wait() once the current thread breaks out of the
wait loop in __wbt_wait. This will ensure new requests always
end up at the back of the queue, and they won't overtake requests
that are already in the wait queue. With that change, the loop
in wbt_wait is also in line with many other wait loops in the kernel.
Waking up just one thread drastically reduces lock contention, as
does moving the wait queue add/remove out of the loop.
A significant drop in lockdep's lock contention numbers is seen when
running the test application on the patched kernel.
Signed-off-by: Anchal Agarwal <anchalag@amazon.com>
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-08-07 23:40:49 +03:00
wake_up ( & rqw - > wait ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
}
/*
* Called on completion of a request . Note that it ' s also called when
* a request is merged , when the request gets freed .
*/
2018-07-03 18:32:35 +03:00
static void wbt_done ( struct rq_qos * rqos , struct request * rq )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
2018-07-03 18:32:35 +03:00
struct rq_wb * rwb = RQWB ( rqos ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
2018-05-09 12:08:48 +03:00
if ( ! wbt_is_tracked ( rq ) ) {
if ( rwb - > sync_cookie = = rq ) {
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
rwb - > sync_issue = 0 ;
rwb - > sync_cookie = NULL ;
}
2018-05-09 12:08:48 +03:00
if ( wbt_is_read ( rq ) )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
wb_timestamp ( rwb , & rwb - > last_comp ) ;
} else {
2018-05-09 12:08:48 +03:00
WARN_ON_ONCE ( rq = = rwb - > sync_cookie ) ;
2018-07-03 18:32:35 +03:00
__wbt_done ( rqos , wbt_flags ( rq ) ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
2018-05-09 12:08:48 +03:00
wbt_clear_state ( rq ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
2016-11-16 18:29:57 +03:00
static inline bool stat_sample_valid ( struct blk_rq_stat * stat )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
/*
* We need at least one read sample , and a minimum of
* RWB_MIN_WRITE_SAMPLES . We require some write samples to know
* that it ' s writes impacting us , and not just some sole read on
* a device that is in a lower power state .
*/
2017-03-21 18:56:06 +03:00
return ( stat [ READ ] . nr_samples > = 1 & &
stat [ WRITE ] . nr_samples > = RWB_MIN_WRITE_SAMPLES ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
static u64 rwb_sync_issue_lat ( struct rq_wb * rwb )
{
locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns to READ_ONCE()/WRITE_ONCE()
Please do not apply this to mainline directly, instead please re-run the
coccinelle script shown below and apply its output.
For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
preference to ACCESS_ONCE(), and new code is expected to use one of the
former. So far, there's been no reason to change most existing uses of
ACCESS_ONCE(), as these aren't harmful, and changing them results in
churn.
However, for some features, the read/write distinction is critical to
correct operation. To distinguish these cases, separate read/write
accessors must be used. This patch migrates (most) remaining
ACCESS_ONCE() instances to {READ,WRITE}_ONCE(), using the following
coccinelle script:
----
// Convert trivial ACCESS_ONCE() uses to equivalent READ_ONCE() and
// WRITE_ONCE()
// $ make coccicheck COCCI=/home/mark/once.cocci SPFLAGS="--include-headers" MODE=patch
virtual patch
@ depends on patch @
expression E1, E2;
@@
- ACCESS_ONCE(E1) = E2
+ WRITE_ONCE(E1, E2)
@ depends on patch @
expression E;
@@
- ACCESS_ONCE(E)
+ READ_ONCE(E)
----
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: davem@davemloft.net
Cc: linux-arch@vger.kernel.org
Cc: mpe@ellerman.id.au
Cc: shuah@kernel.org
Cc: snitzer@redhat.com
Cc: thor.thayer@linux.intel.com
Cc: tj@kernel.org
Cc: viro@zeniv.linux.org.uk
Cc: will.deacon@arm.com
Link: http://lkml.kernel.org/r/1508792849-3115-19-git-send-email-paulmck@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-10-24 00:07:29 +03:00
u64 now , issue = READ_ONCE ( rwb - > sync_issue ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
if ( ! issue | | ! rwb - > sync_cookie )
return 0 ;
now = ktime_to_ns ( ktime_get ( ) ) ;
return now - issue ;
}
enum {
LAT_OK = 1 ,
LAT_UNKNOWN ,
LAT_UNKNOWN_WRITES ,
LAT_EXCEEDED ,
} ;
blk-stat: convert to callback-based statistics reporting
Currently, statistics are gathered in ~0.13s windows, and users grab the
statistics whenever they need them. This is not ideal for both in-tree
users:
1. Writeback throttling wants its own dynamically sized window of
statistics. Since the blk-stats statistics are reset after every
window and the wbt windows don't line up with the blk-stats windows,
wbt doesn't see every I/O.
2. Polling currently grabs the statistics on every I/O. Again, depending
on how the window lines up, we may miss some I/Os. It's also
unnecessary overhead to get the statistics on every I/O; the hybrid
polling heuristic would be just as happy with the statistics from the
previous full window.
This reworks the blk-stats infrastructure to be callback-based: users
register a callback that they want called at a given time with all of
the statistics from the window during which the callback was active.
Users can dynamically bucketize the statistics. wbt and polling both
currently use read vs. write, but polling can be extended to further
subdivide based on request size.
The callbacks are kept on an RCU list, and each callback has percpu
stats buffers. There will only be a few users, so the overhead on the
I/O completion side is low. The stats flushing is also simplified
considerably: since the timer function is responsible for clearing the
statistics, we don't have to worry about stale statistics.
wbt is a trivial conversion. After the conversion, the windowing problem
mentioned above is fixed.
For polling, we register an extra callback that caches the previous
window's statistics in the struct request_queue for the hybrid polling
heuristic to use.
Since we no longer have a single stats buffer for the request queue,
this also removes the sysfs and debugfs stats entries. To replace those,
we add a debugfs entry for the poll statistics.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21 18:56:08 +03:00
static int latency_exceeded ( struct rq_wb * rwb , struct blk_rq_stat * stat )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
2018-07-03 18:32:35 +03:00
struct backing_dev_info * bdi = rwb - > rqos . q - > backing_dev_info ;
struct rq_depth * rqd = & rwb - > rq_depth ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
u64 thislat ;
/*
* If our stored sync issue exceeds the window size , or it
* exceeds our min target AND we haven ' t logged any entries ,
* flag the latency as exceeded . wbt works off completion latencies ,
* but for a flooded device , a single sync IO can take a long time
* to complete after being issued . If this time exceeds our
* monitoring window AND we didn ' t see any other completions in that
* window , then count that sync IO as a violation of the latency .
*/
thislat = rwb_sync_issue_lat ( rwb ) ;
if ( thislat > rwb - > cur_win_nsec | |
2017-03-21 18:56:06 +03:00
( thislat > rwb - > min_lat_nsec & & ! stat [ READ ] . nr_samples ) ) {
2016-11-11 07:52:53 +03:00
trace_wbt_lat ( bdi , thislat ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
return LAT_EXCEEDED ;
}
/*
* No read / write mix , if stat isn ' t valid
*/
if ( ! stat_sample_valid ( stat ) ) {
/*
* If we had writes in this stat window and the window is
* current , we ' re only doing writes . If a task recently
* waited or still has writes in flights , consider us doing
* just writes as well .
*/
blk-stat: convert to callback-based statistics reporting
Currently, statistics are gathered in ~0.13s windows, and users grab the
statistics whenever they need them. This is not ideal for both in-tree
users:
1. Writeback throttling wants its own dynamically sized window of
statistics. Since the blk-stats statistics are reset after every
window and the wbt windows don't line up with the blk-stats windows,
wbt doesn't see every I/O.
2. Polling currently grabs the statistics on every I/O. Again, depending
on how the window lines up, we may miss some I/Os. It's also
unnecessary overhead to get the statistics on every I/O; the hybrid
polling heuristic would be just as happy with the statistics from the
previous full window.
This reworks the blk-stats infrastructure to be callback-based: users
register a callback that they want called at a given time with all of
the statistics from the window during which the callback was active.
Users can dynamically bucketize the statistics. wbt and polling both
currently use read vs. write, but polling can be extended to further
subdivide based on request size.
The callbacks are kept on an RCU list, and each callback has percpu
stats buffers. There will only be a few users, so the overhead on the
I/O completion side is low. The stats flushing is also simplified
considerably: since the timer function is responsible for clearing the
statistics, we don't have to worry about stale statistics.
wbt is a trivial conversion. After the conversion, the windowing problem
mentioned above is fixed.
For polling, we register an extra callback that caches the previous
window's statistics in the struct request_queue for the hybrid polling
heuristic to use.
Since we no longer have a single stats buffer for the request queue,
this also removes the sysfs and debugfs stats entries. To replace those,
we add a debugfs entry for the poll statistics.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21 18:56:08 +03:00
if ( stat [ WRITE ] . nr_samples | | wb_recent_wait ( rwb ) | |
wbt_inflight ( rwb ) )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
return LAT_UNKNOWN_WRITES ;
return LAT_UNKNOWN ;
}
/*
* If the ' min ' latency exceeds our target , step down .
*/
2017-03-21 18:56:06 +03:00
if ( stat [ READ ] . min > rwb - > min_lat_nsec ) {
trace_wbt_lat ( bdi , stat [ READ ] . min ) ;
2016-11-11 07:52:53 +03:00
trace_wbt_stat ( bdi , stat ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
return LAT_EXCEEDED ;
}
2018-07-03 18:32:35 +03:00
if ( rqd - > scale_step )
2016-11-11 07:52:53 +03:00
trace_wbt_stat ( bdi , stat ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
return LAT_OK ;
}
static void rwb_trace_step ( struct rq_wb * rwb , const char * msg )
{
2018-07-03 18:32:35 +03:00
struct backing_dev_info * bdi = rwb - > rqos . q - > backing_dev_info ;
struct rq_depth * rqd = & rwb - > rq_depth ;
2016-11-11 07:52:53 +03:00
2018-07-03 18:32:35 +03:00
trace_wbt_step ( bdi , msg , rqd - > scale_step , rwb - > cur_win_nsec ,
rwb - > wb_background , rwb - > wb_normal , rqd - > max_depth ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
2018-07-03 18:32:35 +03:00
static void calc_wb_limits ( struct rq_wb * rwb )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
2018-07-03 18:32:35 +03:00
if ( rwb - > min_lat_nsec = = 0 ) {
rwb - > wb_normal = rwb - > wb_background = 0 ;
} else if ( rwb - > rq_depth . max_depth < = 2 ) {
rwb - > wb_normal = rwb - > rq_depth . max_depth ;
rwb - > wb_background = 1 ;
} else {
rwb - > wb_normal = ( rwb - > rq_depth . max_depth + 1 ) / 2 ;
rwb - > wb_background = ( rwb - > rq_depth . max_depth + 3 ) / 4 ;
}
}
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
2018-07-03 18:32:35 +03:00
static void scale_up ( struct rq_wb * rwb )
{
rq_depth_scale_up ( & rwb - > rq_depth ) ;
calc_wb_limits ( rwb ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
rwb - > unknown_cnt = 0 ;
2018-07-03 18:32:35 +03:00
rwb_trace_step ( rwb , " scale up " ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
static void scale_down ( struct rq_wb * rwb , bool hard_throttle )
{
2018-07-03 18:32:35 +03:00
rq_depth_scale_down ( & rwb - > rq_depth , hard_throttle ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
calc_wb_limits ( rwb ) ;
2018-07-03 18:32:35 +03:00
rwb - > unknown_cnt = 0 ;
rwb_wake_all ( rwb ) ;
rwb_trace_step ( rwb , " scale down " ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
static void rwb_arm_timer ( struct rq_wb * rwb )
{
2018-07-03 18:32:35 +03:00
struct rq_depth * rqd = & rwb - > rq_depth ;
if ( rqd - > scale_step > 0 ) {
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
/*
* We should speed this up , using some variant of a fast
* integer inverse square root calculation . Since we only do
* this for every window expiration , it ' s not a huge deal ,
* though .
*/
rwb - > cur_win_nsec = div_u64 ( rwb - > win_nsec < < 4 ,
2018-07-03 18:32:35 +03:00
int_sqrt ( ( rqd - > scale_step + 1 ) < < 8 ) ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
} else {
/*
* For step < 0 , we don ' t want to increase / decrease the
* window size .
*/
rwb - > cur_win_nsec = rwb - > win_nsec ;
}
blk-stat: convert to callback-based statistics reporting
Currently, statistics are gathered in ~0.13s windows, and users grab the
statistics whenever they need them. This is not ideal for both in-tree
users:
1. Writeback throttling wants its own dynamically sized window of
statistics. Since the blk-stats statistics are reset after every
window and the wbt windows don't line up with the blk-stats windows,
wbt doesn't see every I/O.
2. Polling currently grabs the statistics on every I/O. Again, depending
on how the window lines up, we may miss some I/Os. It's also
unnecessary overhead to get the statistics on every I/O; the hybrid
polling heuristic would be just as happy with the statistics from the
previous full window.
This reworks the blk-stats infrastructure to be callback-based: users
register a callback that they want called at a given time with all of
the statistics from the window during which the callback was active.
Users can dynamically bucketize the statistics. wbt and polling both
currently use read vs. write, but polling can be extended to further
subdivide based on request size.
The callbacks are kept on an RCU list, and each callback has percpu
stats buffers. There will only be a few users, so the overhead on the
I/O completion side is low. The stats flushing is also simplified
considerably: since the timer function is responsible for clearing the
statistics, we don't have to worry about stale statistics.
wbt is a trivial conversion. After the conversion, the windowing problem
mentioned above is fixed.
For polling, we register an extra callback that caches the previous
window's statistics in the struct request_queue for the hybrid polling
heuristic to use.
Since we no longer have a single stats buffer for the request queue,
this also removes the sysfs and debugfs stats entries. To replace those,
we add a debugfs entry for the poll statistics.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21 18:56:08 +03:00
blk_stat_activate_nsecs ( rwb - > cb , rwb - > cur_win_nsec ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
blk-stat: convert to callback-based statistics reporting
Currently, statistics are gathered in ~0.13s windows, and users grab the
statistics whenever they need them. This is not ideal for both in-tree
users:
1. Writeback throttling wants its own dynamically sized window of
statistics. Since the blk-stats statistics are reset after every
window and the wbt windows don't line up with the blk-stats windows,
wbt doesn't see every I/O.
2. Polling currently grabs the statistics on every I/O. Again, depending
on how the window lines up, we may miss some I/Os. It's also
unnecessary overhead to get the statistics on every I/O; the hybrid
polling heuristic would be just as happy with the statistics from the
previous full window.
This reworks the blk-stats infrastructure to be callback-based: users
register a callback that they want called at a given time with all of
the statistics from the window during which the callback was active.
Users can dynamically bucketize the statistics. wbt and polling both
currently use read vs. write, but polling can be extended to further
subdivide based on request size.
The callbacks are kept on an RCU list, and each callback has percpu
stats buffers. There will only be a few users, so the overhead on the
I/O completion side is low. The stats flushing is also simplified
considerably: since the timer function is responsible for clearing the
statistics, we don't have to worry about stale statistics.
wbt is a trivial conversion. After the conversion, the windowing problem
mentioned above is fixed.
For polling, we register an extra callback that caches the previous
window's statistics in the struct request_queue for the hybrid polling
heuristic to use.
Since we no longer have a single stats buffer for the request queue,
this also removes the sysfs and debugfs stats entries. To replace those,
we add a debugfs entry for the poll statistics.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21 18:56:08 +03:00
static void wb_timer_fn ( struct blk_stat_callback * cb )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
blk-stat: convert to callback-based statistics reporting
Currently, statistics are gathered in ~0.13s windows, and users grab the
statistics whenever they need them. This is not ideal for both in-tree
users:
1. Writeback throttling wants its own dynamically sized window of
statistics. Since the blk-stats statistics are reset after every
window and the wbt windows don't line up with the blk-stats windows,
wbt doesn't see every I/O.
2. Polling currently grabs the statistics on every I/O. Again, depending
on how the window lines up, we may miss some I/Os. It's also
unnecessary overhead to get the statistics on every I/O; the hybrid
polling heuristic would be just as happy with the statistics from the
previous full window.
This reworks the blk-stats infrastructure to be callback-based: users
register a callback that they want called at a given time with all of
the statistics from the window during which the callback was active.
Users can dynamically bucketize the statistics. wbt and polling both
currently use read vs. write, but polling can be extended to further
subdivide based on request size.
The callbacks are kept on an RCU list, and each callback has percpu
stats buffers. There will only be a few users, so the overhead on the
I/O completion side is low. The stats flushing is also simplified
considerably: since the timer function is responsible for clearing the
statistics, we don't have to worry about stale statistics.
wbt is a trivial conversion. After the conversion, the windowing problem
mentioned above is fixed.
For polling, we register an extra callback that caches the previous
window's statistics in the struct request_queue for the hybrid polling
heuristic to use.
Since we no longer have a single stats buffer for the request queue,
this also removes the sysfs and debugfs stats entries. To replace those,
we add a debugfs entry for the poll statistics.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21 18:56:08 +03:00
struct rq_wb * rwb = cb - > data ;
2018-07-03 18:32:35 +03:00
struct rq_depth * rqd = & rwb - > rq_depth ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
unsigned int inflight = wbt_inflight ( rwb ) ;
int status ;
blk-stat: convert to callback-based statistics reporting
Currently, statistics are gathered in ~0.13s windows, and users grab the
statistics whenever they need them. This is not ideal for both in-tree
users:
1. Writeback throttling wants its own dynamically sized window of
statistics. Since the blk-stats statistics are reset after every
window and the wbt windows don't line up with the blk-stats windows,
wbt doesn't see every I/O.
2. Polling currently grabs the statistics on every I/O. Again, depending
on how the window lines up, we may miss some I/Os. It's also
unnecessary overhead to get the statistics on every I/O; the hybrid
polling heuristic would be just as happy with the statistics from the
previous full window.
This reworks the blk-stats infrastructure to be callback-based: users
register a callback that they want called at a given time with all of
the statistics from the window during which the callback was active.
Users can dynamically bucketize the statistics. wbt and polling both
currently use read vs. write, but polling can be extended to further
subdivide based on request size.
The callbacks are kept on an RCU list, and each callback has percpu
stats buffers. There will only be a few users, so the overhead on the
I/O completion side is low. The stats flushing is also simplified
considerably: since the timer function is responsible for clearing the
statistics, we don't have to worry about stale statistics.
wbt is a trivial conversion. After the conversion, the windowing problem
mentioned above is fixed.
For polling, we register an extra callback that caches the previous
window's statistics in the struct request_queue for the hybrid polling
heuristic to use.
Since we no longer have a single stats buffer for the request queue,
this also removes the sysfs and debugfs stats entries. To replace those,
we add a debugfs entry for the poll statistics.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21 18:56:08 +03:00
status = latency_exceeded ( rwb , cb - > stat ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
2018-07-03 18:32:35 +03:00
trace_wbt_timer ( rwb - > rqos . q - > backing_dev_info , status , rqd - > scale_step ,
2016-11-11 07:52:53 +03:00
inflight ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
/*
* If we exceeded the latency target , step down . If we did not ,
* step one level up . If we don ' t know enough to say either exceeded
* or ok , then don ' t do anything .
*/
switch ( status ) {
case LAT_EXCEEDED :
scale_down ( rwb , true ) ;
break ;
case LAT_OK :
scale_up ( rwb ) ;
break ;
case LAT_UNKNOWN_WRITES :
/*
* We started a the center step , but don ' t have a valid
* read / write sample , but we do have writes going on .
* Allow step to go negative , to increase write perf .
*/
scale_up ( rwb ) ;
break ;
case LAT_UNKNOWN :
if ( + + rwb - > unknown_cnt < RWB_UNKNOWN_BUMP )
break ;
/*
* We get here when previously scaled reduced depth , and we
* currently don ' t have a valid read / write sample . For that
* case , slowly return to center state ( step = = 0 ) .
*/
2018-07-03 18:32:35 +03:00
if ( rqd - > scale_step > 0 )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
scale_up ( rwb ) ;
2018-07-03 18:32:35 +03:00
else if ( rqd - > scale_step < 0 )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
scale_down ( rwb , false ) ;
break ;
default :
break ;
}
/*
* Re - arm timer , if we have IO in flight
*/
2018-07-03 18:32:35 +03:00
if ( rqd - > scale_step | | inflight )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
rwb_arm_timer ( rwb ) ;
}
2018-07-03 18:32:35 +03:00
static void __wbt_update_limits ( struct rq_wb * rwb )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
2018-07-03 18:32:35 +03:00
struct rq_depth * rqd = & rwb - > rq_depth ;
rqd - > scale_step = 0 ;
rqd - > scaled_max = false ;
rq_depth_calc_max_depth ( rqd ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
calc_wb_limits ( rwb ) ;
rwb_wake_all ( rwb ) ;
}
2018-07-03 18:32:35 +03:00
void wbt_update_limits ( struct request_queue * q )
{
struct rq_qos * rqos = wbt_rq_qos ( q ) ;
if ( ! rqos )
return ;
__wbt_update_limits ( RQWB ( rqos ) ) ;
}
u64 wbt_get_min_lat ( struct request_queue * q )
{
struct rq_qos * rqos = wbt_rq_qos ( q ) ;
if ( ! rqos )
return 0 ;
return RQWB ( rqos ) - > min_lat_nsec ;
}
void wbt_set_min_lat ( struct request_queue * q , u64 val )
{
struct rq_qos * rqos = wbt_rq_qos ( q ) ;
if ( ! rqos )
return ;
RQWB ( rqos ) - > min_lat_nsec = val ;
RQWB ( rqos ) - > enable_state = WBT_STATE_ON_MANUAL ;
__wbt_update_limits ( RQWB ( rqos ) ) ;
}
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
static bool close_io ( struct rq_wb * rwb )
{
const unsigned long now = jiffies ;
return time_before ( now , rwb - > last_issue + HZ / 10 ) | |
time_before ( now , rwb - > last_comp + HZ / 10 ) ;
}
# define REQ_HIPRIO (REQ_SYNC | REQ_META | REQ_PRIO)
static inline unsigned int get_limit ( struct rq_wb * rwb , unsigned long rw )
{
unsigned int limit ;
2018-08-20 22:24:25 +03:00
/*
* If we got disabled , just return UINT_MAX . This ensures that
* we ' ll properly inc a new IO , and dec + wakeup at the end .
*/
if ( ! rwb_enabled ( rwb ) )
return UINT_MAX ;
2018-05-07 19:03:23 +03:00
if ( ( rw & REQ_OP_MASK ) = = REQ_OP_DISCARD )
return rwb - > wb_background ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
/*
* At this point we know it ' s a buffered write . If this is
2017-11-23 16:40:10 +03:00
* kswapd trying to free memory , or REQ_SYNC is set , then
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
* it ' s WB_SYNC_ALL writeback , and we ' ll use the max limit for
* that . If the write is marked as a background write , then use
* the idle limit , or go to normal if we haven ' t had competing
* IO for a bit .
*/
if ( ( rw & REQ_HIPRIO ) | | wb_recent_wait ( rwb ) | | current_is_kswapd ( ) )
2018-07-03 18:32:35 +03:00
limit = rwb - > rq_depth . max_depth ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
else if ( ( rw & REQ_BACKGROUND ) | | close_io ( rwb ) ) {
/*
* If less than 100 ms since we completed unrelated IO ,
* limit us to half the depth for background writeback .
*/
limit = rwb - > wb_background ;
} else
limit = rwb - > wb_normal ;
return limit ;
}
/*
* Block if we will exceed our limit , or if we are currently waiting for
* the timer to kick off queuing again .
*/
2018-05-07 18:57:08 +03:00
static void __wbt_wait ( struct rq_wb * rwb , enum wbt_flags wb_acct ,
unsigned long rw , spinlock_t * lock )
2017-01-02 19:48:47 +03:00
__releases ( lock )
__acquires ( lock )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
2018-05-07 18:57:08 +03:00
struct rq_wait * rqw = get_rq_wait ( rwb , wb_acct ) ;
blk-wbt: Avoid lock contention and thundering herd issue in wbt_wait
I am currently running a large bare metal instance (i3.metal)
on EC2 with 72 cores, 512GB of RAM and NVME drives, with a
4.18 kernel. I have a workload that simulates a database
workload and I am running into lockup issues when writeback
throttling is enabled,with the hung task detector also
kicking in.
Crash dumps show that most CPUs (up to 50 of them) are
all trying to get the wbt wait queue lock while trying to add
themselves to it in __wbt_wait (see stack traces below).
[ 0.948118] CPU: 45 PID: 0 Comm: swapper/45 Not tainted 4.14.51-62.38.amzn1.x86_64 #1
[ 0.948119] Hardware name: Amazon EC2 i3.metal/Not Specified, BIOS 1.0 10/16/2017
[ 0.948120] task: ffff883f7878c000 task.stack: ffffc9000c69c000
[ 0.948124] RIP: 0010:native_queued_spin_lock_slowpath+0xf8/0x1a0
[ 0.948125] RSP: 0018:ffff883f7fcc3dc8 EFLAGS: 00000046
[ 0.948126] RAX: 0000000000000000 RBX: ffff887f7709ca68 RCX: ffff883f7fce2a00
[ 0.948128] RDX: 000000000000001c RSI: 0000000000740001 RDI: ffff887f7709ca68
[ 0.948129] RBP: 0000000000000002 R08: 0000000000b80000 R09: 0000000000000000
[ 0.948130] R10: ffff883f7fcc3d78 R11: 000000000de27121 R12: 0000000000000002
[ 0.948131] R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000
[ 0.948132] FS: 0000000000000000(0000) GS:ffff883f7fcc0000(0000) knlGS:0000000000000000
[ 0.948134] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.948135] CR2: 000000c424c77000 CR3: 0000000002010005 CR4: 00000000003606e0
[ 0.948136] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.948137] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.948138] Call Trace:
[ 0.948139] <IRQ>
[ 0.948142] do_raw_spin_lock+0xad/0xc0
[ 0.948145] _raw_spin_lock_irqsave+0x44/0x4b
[ 0.948149] ? __wake_up_common_lock+0x53/0x90
[ 0.948150] __wake_up_common_lock+0x53/0x90
[ 0.948155] wbt_done+0x7b/0xa0
[ 0.948158] blk_mq_free_request+0xb7/0x110
[ 0.948161] __blk_mq_complete_request+0xcb/0x140
[ 0.948166] nvme_process_cq+0xce/0x1a0 [nvme]
[ 0.948169] nvme_irq+0x23/0x50 [nvme]
[ 0.948173] __handle_irq_event_percpu+0x46/0x300
[ 0.948176] handle_irq_event_percpu+0x20/0x50
[ 0.948179] handle_irq_event+0x34/0x60
[ 0.948181] handle_edge_irq+0x77/0x190
[ 0.948185] handle_irq+0xaf/0x120
[ 0.948188] do_IRQ+0x53/0x110
[ 0.948191] common_interrupt+0x87/0x87
[ 0.948192] </IRQ>
....
[ 0.311136] CPU: 4 PID: 9737 Comm: run_linux_amd64 Not tainted 4.14.51-62.38.amzn1.x86_64 #1
[ 0.311137] Hardware name: Amazon EC2 i3.metal/Not Specified, BIOS 1.0 10/16/2017
[ 0.311138] task: ffff883f6e6a8000 task.stack: ffffc9000f1ec000
[ 0.311141] RIP: 0010:native_queued_spin_lock_slowpath+0xf5/0x1a0
[ 0.311142] RSP: 0018:ffffc9000f1efa28 EFLAGS: 00000046
[ 0.311144] RAX: 0000000000000000 RBX: ffff887f7709ca68 RCX: ffff883f7f722a00
[ 0.311145] RDX: 0000000000000035 RSI: 0000000000d80001 RDI: ffff887f7709ca68
[ 0.311146] RBP: 0000000000000202 R08: 0000000000140000 R09: 0000000000000000
[ 0.311147] R10: ffffc9000f1ef9d8 R11: 000000001a249fa0 R12: ffff887f7709ca68
[ 0.311148] R13: ffffc9000f1efad0 R14: 0000000000000000 R15: ffff887f7709ca00
[ 0.311149] FS: 000000c423f30090(0000) GS:ffff883f7f700000(0000) knlGS:0000000000000000
[ 0.311150] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.311151] CR2: 00007feefcea4000 CR3: 0000007f7016e001 CR4: 00000000003606e0
[ 0.311152] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.311153] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.311154] Call Trace:
[ 0.311157] do_raw_spin_lock+0xad/0xc0
[ 0.311160] _raw_spin_lock_irqsave+0x44/0x4b
[ 0.311162] ? prepare_to_wait_exclusive+0x28/0xb0
[ 0.311164] prepare_to_wait_exclusive+0x28/0xb0
[ 0.311167] wbt_wait+0x127/0x330
[ 0.311169] ? finish_wait+0x80/0x80
[ 0.311172] ? generic_make_request+0xda/0x3b0
[ 0.311174] blk_mq_make_request+0xd6/0x7b0
[ 0.311176] ? blk_queue_enter+0x24/0x260
[ 0.311178] ? generic_make_request+0xda/0x3b0
[ 0.311181] generic_make_request+0x10c/0x3b0
[ 0.311183] ? submit_bio+0x5c/0x110
[ 0.311185] submit_bio+0x5c/0x110
[ 0.311197] ? __ext4_journal_stop+0x36/0xa0 [ext4]
[ 0.311210] ext4_io_submit+0x48/0x60 [ext4]
[ 0.311222] ext4_writepages+0x810/0x11f0 [ext4]
[ 0.311229] ? do_writepages+0x3c/0xd0
[ 0.311239] ? ext4_mark_inode_dirty+0x260/0x260 [ext4]
[ 0.311240] do_writepages+0x3c/0xd0
[ 0.311243] ? _raw_spin_unlock+0x24/0x30
[ 0.311245] ? wbc_attach_and_unlock_inode+0x165/0x280
[ 0.311248] ? __filemap_fdatawrite_range+0xa3/0xe0
[ 0.311250] __filemap_fdatawrite_range+0xa3/0xe0
[ 0.311253] file_write_and_wait_range+0x34/0x90
[ 0.311264] ext4_sync_file+0x151/0x500 [ext4]
[ 0.311267] do_fsync+0x38/0x60
[ 0.311270] SyS_fsync+0xc/0x10
[ 0.311272] do_syscall_64+0x6f/0x170
[ 0.311274] entry_SYSCALL_64_after_hwframe+0x42/0xb7
In the original patch, wbt_done is waking up all the exclusive
processes in the wait queue, which can cause a thundering herd
if there is a large number of writer threads in the queue. The
original intention of the code seems to be to wake up one thread
only however, it uses wake_up_all() in __wbt_done(), and then
uses the following check in __wbt_wait to have only one thread
actually get out of the wait loop:
if (waitqueue_active(&rqw->wait) &&
rqw->wait.head.next != &wait->entry)
return false;
The problem with this is that the wait entry in wbt_wait is
define with DEFINE_WAIT, which uses the autoremove wakeup function.
That means that the above check is invalid - the wait entry will
have been removed from the queue already by the time we hit the
check in the loop.
Secondly, auto-removing the wait entries also means that the wait
queue essentially gets reordered "randomly" (e.g. threads re-add
themselves in the order they got to run after being woken up).
Additionally, new requests entering wbt_wait might overtake requests
that were queued earlier, because the wait queue will be
(temporarily) empty after the wake_up_all, so the waitqueue_active
check will not stop them. This can cause certain threads to starve
under high load.
The fix is to leave the woken up requests in the queue and remove
them in finish_wait() once the current thread breaks out of the
wait loop in __wbt_wait. This will ensure new requests always
end up at the back of the queue, and they won't overtake requests
that are already in the wait queue. With that change, the loop
in wbt_wait is also in line with many other wait loops in the kernel.
Waking up just one thread drastically reduces lock contention, as
does moving the wait queue add/remove out of the loop.
A significant drop in lockdep's lock contention numbers is seen when
running the test application on the patched kernel.
Signed-off-by: Anchal Agarwal <anchalag@amazon.com>
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-08-07 23:40:49 +03:00
DECLARE_WAITQUEUE ( wait , current ) ;
2018-08-20 22:22:27 +03:00
bool has_sleeper ;
blk-wbt: Avoid lock contention and thundering herd issue in wbt_wait
I am currently running a large bare metal instance (i3.metal)
on EC2 with 72 cores, 512GB of RAM and NVME drives, with a
4.18 kernel. I have a workload that simulates a database
workload and I am running into lockup issues when writeback
throttling is enabled,with the hung task detector also
kicking in.
Crash dumps show that most CPUs (up to 50 of them) are
all trying to get the wbt wait queue lock while trying to add
themselves to it in __wbt_wait (see stack traces below).
[ 0.948118] CPU: 45 PID: 0 Comm: swapper/45 Not tainted 4.14.51-62.38.amzn1.x86_64 #1
[ 0.948119] Hardware name: Amazon EC2 i3.metal/Not Specified, BIOS 1.0 10/16/2017
[ 0.948120] task: ffff883f7878c000 task.stack: ffffc9000c69c000
[ 0.948124] RIP: 0010:native_queued_spin_lock_slowpath+0xf8/0x1a0
[ 0.948125] RSP: 0018:ffff883f7fcc3dc8 EFLAGS: 00000046
[ 0.948126] RAX: 0000000000000000 RBX: ffff887f7709ca68 RCX: ffff883f7fce2a00
[ 0.948128] RDX: 000000000000001c RSI: 0000000000740001 RDI: ffff887f7709ca68
[ 0.948129] RBP: 0000000000000002 R08: 0000000000b80000 R09: 0000000000000000
[ 0.948130] R10: ffff883f7fcc3d78 R11: 000000000de27121 R12: 0000000000000002
[ 0.948131] R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000
[ 0.948132] FS: 0000000000000000(0000) GS:ffff883f7fcc0000(0000) knlGS:0000000000000000
[ 0.948134] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.948135] CR2: 000000c424c77000 CR3: 0000000002010005 CR4: 00000000003606e0
[ 0.948136] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.948137] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.948138] Call Trace:
[ 0.948139] <IRQ>
[ 0.948142] do_raw_spin_lock+0xad/0xc0
[ 0.948145] _raw_spin_lock_irqsave+0x44/0x4b
[ 0.948149] ? __wake_up_common_lock+0x53/0x90
[ 0.948150] __wake_up_common_lock+0x53/0x90
[ 0.948155] wbt_done+0x7b/0xa0
[ 0.948158] blk_mq_free_request+0xb7/0x110
[ 0.948161] __blk_mq_complete_request+0xcb/0x140
[ 0.948166] nvme_process_cq+0xce/0x1a0 [nvme]
[ 0.948169] nvme_irq+0x23/0x50 [nvme]
[ 0.948173] __handle_irq_event_percpu+0x46/0x300
[ 0.948176] handle_irq_event_percpu+0x20/0x50
[ 0.948179] handle_irq_event+0x34/0x60
[ 0.948181] handle_edge_irq+0x77/0x190
[ 0.948185] handle_irq+0xaf/0x120
[ 0.948188] do_IRQ+0x53/0x110
[ 0.948191] common_interrupt+0x87/0x87
[ 0.948192] </IRQ>
....
[ 0.311136] CPU: 4 PID: 9737 Comm: run_linux_amd64 Not tainted 4.14.51-62.38.amzn1.x86_64 #1
[ 0.311137] Hardware name: Amazon EC2 i3.metal/Not Specified, BIOS 1.0 10/16/2017
[ 0.311138] task: ffff883f6e6a8000 task.stack: ffffc9000f1ec000
[ 0.311141] RIP: 0010:native_queued_spin_lock_slowpath+0xf5/0x1a0
[ 0.311142] RSP: 0018:ffffc9000f1efa28 EFLAGS: 00000046
[ 0.311144] RAX: 0000000000000000 RBX: ffff887f7709ca68 RCX: ffff883f7f722a00
[ 0.311145] RDX: 0000000000000035 RSI: 0000000000d80001 RDI: ffff887f7709ca68
[ 0.311146] RBP: 0000000000000202 R08: 0000000000140000 R09: 0000000000000000
[ 0.311147] R10: ffffc9000f1ef9d8 R11: 000000001a249fa0 R12: ffff887f7709ca68
[ 0.311148] R13: ffffc9000f1efad0 R14: 0000000000000000 R15: ffff887f7709ca00
[ 0.311149] FS: 000000c423f30090(0000) GS:ffff883f7f700000(0000) knlGS:0000000000000000
[ 0.311150] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.311151] CR2: 00007feefcea4000 CR3: 0000007f7016e001 CR4: 00000000003606e0
[ 0.311152] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.311153] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.311154] Call Trace:
[ 0.311157] do_raw_spin_lock+0xad/0xc0
[ 0.311160] _raw_spin_lock_irqsave+0x44/0x4b
[ 0.311162] ? prepare_to_wait_exclusive+0x28/0xb0
[ 0.311164] prepare_to_wait_exclusive+0x28/0xb0
[ 0.311167] wbt_wait+0x127/0x330
[ 0.311169] ? finish_wait+0x80/0x80
[ 0.311172] ? generic_make_request+0xda/0x3b0
[ 0.311174] blk_mq_make_request+0xd6/0x7b0
[ 0.311176] ? blk_queue_enter+0x24/0x260
[ 0.311178] ? generic_make_request+0xda/0x3b0
[ 0.311181] generic_make_request+0x10c/0x3b0
[ 0.311183] ? submit_bio+0x5c/0x110
[ 0.311185] submit_bio+0x5c/0x110
[ 0.311197] ? __ext4_journal_stop+0x36/0xa0 [ext4]
[ 0.311210] ext4_io_submit+0x48/0x60 [ext4]
[ 0.311222] ext4_writepages+0x810/0x11f0 [ext4]
[ 0.311229] ? do_writepages+0x3c/0xd0
[ 0.311239] ? ext4_mark_inode_dirty+0x260/0x260 [ext4]
[ 0.311240] do_writepages+0x3c/0xd0
[ 0.311243] ? _raw_spin_unlock+0x24/0x30
[ 0.311245] ? wbc_attach_and_unlock_inode+0x165/0x280
[ 0.311248] ? __filemap_fdatawrite_range+0xa3/0xe0
[ 0.311250] __filemap_fdatawrite_range+0xa3/0xe0
[ 0.311253] file_write_and_wait_range+0x34/0x90
[ 0.311264] ext4_sync_file+0x151/0x500 [ext4]
[ 0.311267] do_fsync+0x38/0x60
[ 0.311270] SyS_fsync+0xc/0x10
[ 0.311272] do_syscall_64+0x6f/0x170
[ 0.311274] entry_SYSCALL_64_after_hwframe+0x42/0xb7
In the original patch, wbt_done is waking up all the exclusive
processes in the wait queue, which can cause a thundering herd
if there is a large number of writer threads in the queue. The
original intention of the code seems to be to wake up one thread
only however, it uses wake_up_all() in __wbt_done(), and then
uses the following check in __wbt_wait to have only one thread
actually get out of the wait loop:
if (waitqueue_active(&rqw->wait) &&
rqw->wait.head.next != &wait->entry)
return false;
The problem with this is that the wait entry in wbt_wait is
define with DEFINE_WAIT, which uses the autoremove wakeup function.
That means that the above check is invalid - the wait entry will
have been removed from the queue already by the time we hit the
check in the loop.
Secondly, auto-removing the wait entries also means that the wait
queue essentially gets reordered "randomly" (e.g. threads re-add
themselves in the order they got to run after being woken up).
Additionally, new requests entering wbt_wait might overtake requests
that were queued earlier, because the wait queue will be
(temporarily) empty after the wake_up_all, so the waitqueue_active
check will not stop them. This can cause certain threads to starve
under high load.
The fix is to leave the woken up requests in the queue and remove
them in finish_wait() once the current thread breaks out of the
wait loop in __wbt_wait. This will ensure new requests always
end up at the back of the queue, and they won't overtake requests
that are already in the wait queue. With that change, the loop
in wbt_wait is also in line with many other wait loops in the kernel.
Waking up just one thread drastically reduces lock contention, as
does moving the wait queue add/remove out of the loop.
A significant drop in lockdep's lock contention numbers is seen when
running the test application on the patched kernel.
Signed-off-by: Anchal Agarwal <anchalag@amazon.com>
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-08-07 23:40:49 +03:00
2018-08-20 22:22:27 +03:00
has_sleeper = wq_has_sleeper ( & rqw - > wait ) ;
if ( ! has_sleeper & & rq_wait_inc_below ( rqw , get_limit ( rwb , rw ) ) )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
return ;
blk-wbt: Avoid lock contention and thundering herd issue in wbt_wait
I am currently running a large bare metal instance (i3.metal)
on EC2 with 72 cores, 512GB of RAM and NVME drives, with a
4.18 kernel. I have a workload that simulates a database
workload and I am running into lockup issues when writeback
throttling is enabled,with the hung task detector also
kicking in.
Crash dumps show that most CPUs (up to 50 of them) are
all trying to get the wbt wait queue lock while trying to add
themselves to it in __wbt_wait (see stack traces below).
[ 0.948118] CPU: 45 PID: 0 Comm: swapper/45 Not tainted 4.14.51-62.38.amzn1.x86_64 #1
[ 0.948119] Hardware name: Amazon EC2 i3.metal/Not Specified, BIOS 1.0 10/16/2017
[ 0.948120] task: ffff883f7878c000 task.stack: ffffc9000c69c000
[ 0.948124] RIP: 0010:native_queued_spin_lock_slowpath+0xf8/0x1a0
[ 0.948125] RSP: 0018:ffff883f7fcc3dc8 EFLAGS: 00000046
[ 0.948126] RAX: 0000000000000000 RBX: ffff887f7709ca68 RCX: ffff883f7fce2a00
[ 0.948128] RDX: 000000000000001c RSI: 0000000000740001 RDI: ffff887f7709ca68
[ 0.948129] RBP: 0000000000000002 R08: 0000000000b80000 R09: 0000000000000000
[ 0.948130] R10: ffff883f7fcc3d78 R11: 000000000de27121 R12: 0000000000000002
[ 0.948131] R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000
[ 0.948132] FS: 0000000000000000(0000) GS:ffff883f7fcc0000(0000) knlGS:0000000000000000
[ 0.948134] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.948135] CR2: 000000c424c77000 CR3: 0000000002010005 CR4: 00000000003606e0
[ 0.948136] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.948137] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.948138] Call Trace:
[ 0.948139] <IRQ>
[ 0.948142] do_raw_spin_lock+0xad/0xc0
[ 0.948145] _raw_spin_lock_irqsave+0x44/0x4b
[ 0.948149] ? __wake_up_common_lock+0x53/0x90
[ 0.948150] __wake_up_common_lock+0x53/0x90
[ 0.948155] wbt_done+0x7b/0xa0
[ 0.948158] blk_mq_free_request+0xb7/0x110
[ 0.948161] __blk_mq_complete_request+0xcb/0x140
[ 0.948166] nvme_process_cq+0xce/0x1a0 [nvme]
[ 0.948169] nvme_irq+0x23/0x50 [nvme]
[ 0.948173] __handle_irq_event_percpu+0x46/0x300
[ 0.948176] handle_irq_event_percpu+0x20/0x50
[ 0.948179] handle_irq_event+0x34/0x60
[ 0.948181] handle_edge_irq+0x77/0x190
[ 0.948185] handle_irq+0xaf/0x120
[ 0.948188] do_IRQ+0x53/0x110
[ 0.948191] common_interrupt+0x87/0x87
[ 0.948192] </IRQ>
....
[ 0.311136] CPU: 4 PID: 9737 Comm: run_linux_amd64 Not tainted 4.14.51-62.38.amzn1.x86_64 #1
[ 0.311137] Hardware name: Amazon EC2 i3.metal/Not Specified, BIOS 1.0 10/16/2017
[ 0.311138] task: ffff883f6e6a8000 task.stack: ffffc9000f1ec000
[ 0.311141] RIP: 0010:native_queued_spin_lock_slowpath+0xf5/0x1a0
[ 0.311142] RSP: 0018:ffffc9000f1efa28 EFLAGS: 00000046
[ 0.311144] RAX: 0000000000000000 RBX: ffff887f7709ca68 RCX: ffff883f7f722a00
[ 0.311145] RDX: 0000000000000035 RSI: 0000000000d80001 RDI: ffff887f7709ca68
[ 0.311146] RBP: 0000000000000202 R08: 0000000000140000 R09: 0000000000000000
[ 0.311147] R10: ffffc9000f1ef9d8 R11: 000000001a249fa0 R12: ffff887f7709ca68
[ 0.311148] R13: ffffc9000f1efad0 R14: 0000000000000000 R15: ffff887f7709ca00
[ 0.311149] FS: 000000c423f30090(0000) GS:ffff883f7f700000(0000) knlGS:0000000000000000
[ 0.311150] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.311151] CR2: 00007feefcea4000 CR3: 0000007f7016e001 CR4: 00000000003606e0
[ 0.311152] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.311153] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.311154] Call Trace:
[ 0.311157] do_raw_spin_lock+0xad/0xc0
[ 0.311160] _raw_spin_lock_irqsave+0x44/0x4b
[ 0.311162] ? prepare_to_wait_exclusive+0x28/0xb0
[ 0.311164] prepare_to_wait_exclusive+0x28/0xb0
[ 0.311167] wbt_wait+0x127/0x330
[ 0.311169] ? finish_wait+0x80/0x80
[ 0.311172] ? generic_make_request+0xda/0x3b0
[ 0.311174] blk_mq_make_request+0xd6/0x7b0
[ 0.311176] ? blk_queue_enter+0x24/0x260
[ 0.311178] ? generic_make_request+0xda/0x3b0
[ 0.311181] generic_make_request+0x10c/0x3b0
[ 0.311183] ? submit_bio+0x5c/0x110
[ 0.311185] submit_bio+0x5c/0x110
[ 0.311197] ? __ext4_journal_stop+0x36/0xa0 [ext4]
[ 0.311210] ext4_io_submit+0x48/0x60 [ext4]
[ 0.311222] ext4_writepages+0x810/0x11f0 [ext4]
[ 0.311229] ? do_writepages+0x3c/0xd0
[ 0.311239] ? ext4_mark_inode_dirty+0x260/0x260 [ext4]
[ 0.311240] do_writepages+0x3c/0xd0
[ 0.311243] ? _raw_spin_unlock+0x24/0x30
[ 0.311245] ? wbc_attach_and_unlock_inode+0x165/0x280
[ 0.311248] ? __filemap_fdatawrite_range+0xa3/0xe0
[ 0.311250] __filemap_fdatawrite_range+0xa3/0xe0
[ 0.311253] file_write_and_wait_range+0x34/0x90
[ 0.311264] ext4_sync_file+0x151/0x500 [ext4]
[ 0.311267] do_fsync+0x38/0x60
[ 0.311270] SyS_fsync+0xc/0x10
[ 0.311272] do_syscall_64+0x6f/0x170
[ 0.311274] entry_SYSCALL_64_after_hwframe+0x42/0xb7
In the original patch, wbt_done is waking up all the exclusive
processes in the wait queue, which can cause a thundering herd
if there is a large number of writer threads in the queue. The
original intention of the code seems to be to wake up one thread
only however, it uses wake_up_all() in __wbt_done(), and then
uses the following check in __wbt_wait to have only one thread
actually get out of the wait loop:
if (waitqueue_active(&rqw->wait) &&
rqw->wait.head.next != &wait->entry)
return false;
The problem with this is that the wait entry in wbt_wait is
define with DEFINE_WAIT, which uses the autoremove wakeup function.
That means that the above check is invalid - the wait entry will
have been removed from the queue already by the time we hit the
check in the loop.
Secondly, auto-removing the wait entries also means that the wait
queue essentially gets reordered "randomly" (e.g. threads re-add
themselves in the order they got to run after being woken up).
Additionally, new requests entering wbt_wait might overtake requests
that were queued earlier, because the wait queue will be
(temporarily) empty after the wake_up_all, so the waitqueue_active
check will not stop them. This can cause certain threads to starve
under high load.
The fix is to leave the woken up requests in the queue and remove
them in finish_wait() once the current thread breaks out of the
wait loop in __wbt_wait. This will ensure new requests always
end up at the back of the queue, and they won't overtake requests
that are already in the wait queue. With that change, the loop
in wbt_wait is also in line with many other wait loops in the kernel.
Waking up just one thread drastically reduces lock contention, as
does moving the wait queue add/remove out of the loop.
A significant drop in lockdep's lock contention numbers is seen when
running the test application on the patched kernel.
Signed-off-by: Anchal Agarwal <anchalag@amazon.com>
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-08-07 23:40:49 +03:00
add_wait_queue_exclusive ( & rqw - > wait , & wait ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
do {
blk-wbt: Avoid lock contention and thundering herd issue in wbt_wait
I am currently running a large bare metal instance (i3.metal)
on EC2 with 72 cores, 512GB of RAM and NVME drives, with a
4.18 kernel. I have a workload that simulates a database
workload and I am running into lockup issues when writeback
throttling is enabled,with the hung task detector also
kicking in.
Crash dumps show that most CPUs (up to 50 of them) are
all trying to get the wbt wait queue lock while trying to add
themselves to it in __wbt_wait (see stack traces below).
[ 0.948118] CPU: 45 PID: 0 Comm: swapper/45 Not tainted 4.14.51-62.38.amzn1.x86_64 #1
[ 0.948119] Hardware name: Amazon EC2 i3.metal/Not Specified, BIOS 1.0 10/16/2017
[ 0.948120] task: ffff883f7878c000 task.stack: ffffc9000c69c000
[ 0.948124] RIP: 0010:native_queued_spin_lock_slowpath+0xf8/0x1a0
[ 0.948125] RSP: 0018:ffff883f7fcc3dc8 EFLAGS: 00000046
[ 0.948126] RAX: 0000000000000000 RBX: ffff887f7709ca68 RCX: ffff883f7fce2a00
[ 0.948128] RDX: 000000000000001c RSI: 0000000000740001 RDI: ffff887f7709ca68
[ 0.948129] RBP: 0000000000000002 R08: 0000000000b80000 R09: 0000000000000000
[ 0.948130] R10: ffff883f7fcc3d78 R11: 000000000de27121 R12: 0000000000000002
[ 0.948131] R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000
[ 0.948132] FS: 0000000000000000(0000) GS:ffff883f7fcc0000(0000) knlGS:0000000000000000
[ 0.948134] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.948135] CR2: 000000c424c77000 CR3: 0000000002010005 CR4: 00000000003606e0
[ 0.948136] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.948137] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.948138] Call Trace:
[ 0.948139] <IRQ>
[ 0.948142] do_raw_spin_lock+0xad/0xc0
[ 0.948145] _raw_spin_lock_irqsave+0x44/0x4b
[ 0.948149] ? __wake_up_common_lock+0x53/0x90
[ 0.948150] __wake_up_common_lock+0x53/0x90
[ 0.948155] wbt_done+0x7b/0xa0
[ 0.948158] blk_mq_free_request+0xb7/0x110
[ 0.948161] __blk_mq_complete_request+0xcb/0x140
[ 0.948166] nvme_process_cq+0xce/0x1a0 [nvme]
[ 0.948169] nvme_irq+0x23/0x50 [nvme]
[ 0.948173] __handle_irq_event_percpu+0x46/0x300
[ 0.948176] handle_irq_event_percpu+0x20/0x50
[ 0.948179] handle_irq_event+0x34/0x60
[ 0.948181] handle_edge_irq+0x77/0x190
[ 0.948185] handle_irq+0xaf/0x120
[ 0.948188] do_IRQ+0x53/0x110
[ 0.948191] common_interrupt+0x87/0x87
[ 0.948192] </IRQ>
....
[ 0.311136] CPU: 4 PID: 9737 Comm: run_linux_amd64 Not tainted 4.14.51-62.38.amzn1.x86_64 #1
[ 0.311137] Hardware name: Amazon EC2 i3.metal/Not Specified, BIOS 1.0 10/16/2017
[ 0.311138] task: ffff883f6e6a8000 task.stack: ffffc9000f1ec000
[ 0.311141] RIP: 0010:native_queued_spin_lock_slowpath+0xf5/0x1a0
[ 0.311142] RSP: 0018:ffffc9000f1efa28 EFLAGS: 00000046
[ 0.311144] RAX: 0000000000000000 RBX: ffff887f7709ca68 RCX: ffff883f7f722a00
[ 0.311145] RDX: 0000000000000035 RSI: 0000000000d80001 RDI: ffff887f7709ca68
[ 0.311146] RBP: 0000000000000202 R08: 0000000000140000 R09: 0000000000000000
[ 0.311147] R10: ffffc9000f1ef9d8 R11: 000000001a249fa0 R12: ffff887f7709ca68
[ 0.311148] R13: ffffc9000f1efad0 R14: 0000000000000000 R15: ffff887f7709ca00
[ 0.311149] FS: 000000c423f30090(0000) GS:ffff883f7f700000(0000) knlGS:0000000000000000
[ 0.311150] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.311151] CR2: 00007feefcea4000 CR3: 0000007f7016e001 CR4: 00000000003606e0
[ 0.311152] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.311153] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.311154] Call Trace:
[ 0.311157] do_raw_spin_lock+0xad/0xc0
[ 0.311160] _raw_spin_lock_irqsave+0x44/0x4b
[ 0.311162] ? prepare_to_wait_exclusive+0x28/0xb0
[ 0.311164] prepare_to_wait_exclusive+0x28/0xb0
[ 0.311167] wbt_wait+0x127/0x330
[ 0.311169] ? finish_wait+0x80/0x80
[ 0.311172] ? generic_make_request+0xda/0x3b0
[ 0.311174] blk_mq_make_request+0xd6/0x7b0
[ 0.311176] ? blk_queue_enter+0x24/0x260
[ 0.311178] ? generic_make_request+0xda/0x3b0
[ 0.311181] generic_make_request+0x10c/0x3b0
[ 0.311183] ? submit_bio+0x5c/0x110
[ 0.311185] submit_bio+0x5c/0x110
[ 0.311197] ? __ext4_journal_stop+0x36/0xa0 [ext4]
[ 0.311210] ext4_io_submit+0x48/0x60 [ext4]
[ 0.311222] ext4_writepages+0x810/0x11f0 [ext4]
[ 0.311229] ? do_writepages+0x3c/0xd0
[ 0.311239] ? ext4_mark_inode_dirty+0x260/0x260 [ext4]
[ 0.311240] do_writepages+0x3c/0xd0
[ 0.311243] ? _raw_spin_unlock+0x24/0x30
[ 0.311245] ? wbc_attach_and_unlock_inode+0x165/0x280
[ 0.311248] ? __filemap_fdatawrite_range+0xa3/0xe0
[ 0.311250] __filemap_fdatawrite_range+0xa3/0xe0
[ 0.311253] file_write_and_wait_range+0x34/0x90
[ 0.311264] ext4_sync_file+0x151/0x500 [ext4]
[ 0.311267] do_fsync+0x38/0x60
[ 0.311270] SyS_fsync+0xc/0x10
[ 0.311272] do_syscall_64+0x6f/0x170
[ 0.311274] entry_SYSCALL_64_after_hwframe+0x42/0xb7
In the original patch, wbt_done is waking up all the exclusive
processes in the wait queue, which can cause a thundering herd
if there is a large number of writer threads in the queue. The
original intention of the code seems to be to wake up one thread
only however, it uses wake_up_all() in __wbt_done(), and then
uses the following check in __wbt_wait to have only one thread
actually get out of the wait loop:
if (waitqueue_active(&rqw->wait) &&
rqw->wait.head.next != &wait->entry)
return false;
The problem with this is that the wait entry in wbt_wait is
define with DEFINE_WAIT, which uses the autoremove wakeup function.
That means that the above check is invalid - the wait entry will
have been removed from the queue already by the time we hit the
check in the loop.
Secondly, auto-removing the wait entries also means that the wait
queue essentially gets reordered "randomly" (e.g. threads re-add
themselves in the order they got to run after being woken up).
Additionally, new requests entering wbt_wait might overtake requests
that were queued earlier, because the wait queue will be
(temporarily) empty after the wake_up_all, so the waitqueue_active
check will not stop them. This can cause certain threads to starve
under high load.
The fix is to leave the woken up requests in the queue and remove
them in finish_wait() once the current thread breaks out of the
wait loop in __wbt_wait. This will ensure new requests always
end up at the back of the queue, and they won't overtake requests
that are already in the wait queue. With that change, the loop
in wbt_wait is also in line with many other wait loops in the kernel.
Waking up just one thread drastically reduces lock contention, as
does moving the wait queue add/remove out of the loop.
A significant drop in lockdep's lock contention numbers is seen when
running the test application on the patched kernel.
Signed-off-by: Anchal Agarwal <anchalag@amazon.com>
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-08-07 23:40:49 +03:00
set_current_state ( TASK_UNINTERRUPTIBLE ) ;
2018-08-20 22:22:27 +03:00
if ( ! has_sleeper & & rq_wait_inc_below ( rqw , get_limit ( rwb , rw ) ) )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
break ;
2017-01-02 19:48:47 +03:00
if ( lock ) {
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
spin_unlock_irq ( lock ) ;
2017-01-02 19:48:47 +03:00
io_schedule ( ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
spin_lock_irq ( lock ) ;
2017-01-02 19:48:47 +03:00
} else
io_schedule ( ) ;
2018-08-20 22:22:27 +03:00
has_sleeper = false ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
} while ( 1 ) ;
blk-wbt: Avoid lock contention and thundering herd issue in wbt_wait
I am currently running a large bare metal instance (i3.metal)
on EC2 with 72 cores, 512GB of RAM and NVME drives, with a
4.18 kernel. I have a workload that simulates a database
workload and I am running into lockup issues when writeback
throttling is enabled,with the hung task detector also
kicking in.
Crash dumps show that most CPUs (up to 50 of them) are
all trying to get the wbt wait queue lock while trying to add
themselves to it in __wbt_wait (see stack traces below).
[ 0.948118] CPU: 45 PID: 0 Comm: swapper/45 Not tainted 4.14.51-62.38.amzn1.x86_64 #1
[ 0.948119] Hardware name: Amazon EC2 i3.metal/Not Specified, BIOS 1.0 10/16/2017
[ 0.948120] task: ffff883f7878c000 task.stack: ffffc9000c69c000
[ 0.948124] RIP: 0010:native_queued_spin_lock_slowpath+0xf8/0x1a0
[ 0.948125] RSP: 0018:ffff883f7fcc3dc8 EFLAGS: 00000046
[ 0.948126] RAX: 0000000000000000 RBX: ffff887f7709ca68 RCX: ffff883f7fce2a00
[ 0.948128] RDX: 000000000000001c RSI: 0000000000740001 RDI: ffff887f7709ca68
[ 0.948129] RBP: 0000000000000002 R08: 0000000000b80000 R09: 0000000000000000
[ 0.948130] R10: ffff883f7fcc3d78 R11: 000000000de27121 R12: 0000000000000002
[ 0.948131] R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000
[ 0.948132] FS: 0000000000000000(0000) GS:ffff883f7fcc0000(0000) knlGS:0000000000000000
[ 0.948134] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.948135] CR2: 000000c424c77000 CR3: 0000000002010005 CR4: 00000000003606e0
[ 0.948136] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.948137] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.948138] Call Trace:
[ 0.948139] <IRQ>
[ 0.948142] do_raw_spin_lock+0xad/0xc0
[ 0.948145] _raw_spin_lock_irqsave+0x44/0x4b
[ 0.948149] ? __wake_up_common_lock+0x53/0x90
[ 0.948150] __wake_up_common_lock+0x53/0x90
[ 0.948155] wbt_done+0x7b/0xa0
[ 0.948158] blk_mq_free_request+0xb7/0x110
[ 0.948161] __blk_mq_complete_request+0xcb/0x140
[ 0.948166] nvme_process_cq+0xce/0x1a0 [nvme]
[ 0.948169] nvme_irq+0x23/0x50 [nvme]
[ 0.948173] __handle_irq_event_percpu+0x46/0x300
[ 0.948176] handle_irq_event_percpu+0x20/0x50
[ 0.948179] handle_irq_event+0x34/0x60
[ 0.948181] handle_edge_irq+0x77/0x190
[ 0.948185] handle_irq+0xaf/0x120
[ 0.948188] do_IRQ+0x53/0x110
[ 0.948191] common_interrupt+0x87/0x87
[ 0.948192] </IRQ>
....
[ 0.311136] CPU: 4 PID: 9737 Comm: run_linux_amd64 Not tainted 4.14.51-62.38.amzn1.x86_64 #1
[ 0.311137] Hardware name: Amazon EC2 i3.metal/Not Specified, BIOS 1.0 10/16/2017
[ 0.311138] task: ffff883f6e6a8000 task.stack: ffffc9000f1ec000
[ 0.311141] RIP: 0010:native_queued_spin_lock_slowpath+0xf5/0x1a0
[ 0.311142] RSP: 0018:ffffc9000f1efa28 EFLAGS: 00000046
[ 0.311144] RAX: 0000000000000000 RBX: ffff887f7709ca68 RCX: ffff883f7f722a00
[ 0.311145] RDX: 0000000000000035 RSI: 0000000000d80001 RDI: ffff887f7709ca68
[ 0.311146] RBP: 0000000000000202 R08: 0000000000140000 R09: 0000000000000000
[ 0.311147] R10: ffffc9000f1ef9d8 R11: 000000001a249fa0 R12: ffff887f7709ca68
[ 0.311148] R13: ffffc9000f1efad0 R14: 0000000000000000 R15: ffff887f7709ca00
[ 0.311149] FS: 000000c423f30090(0000) GS:ffff883f7f700000(0000) knlGS:0000000000000000
[ 0.311150] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 0.311151] CR2: 00007feefcea4000 CR3: 0000007f7016e001 CR4: 00000000003606e0
[ 0.311152] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.311153] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 0.311154] Call Trace:
[ 0.311157] do_raw_spin_lock+0xad/0xc0
[ 0.311160] _raw_spin_lock_irqsave+0x44/0x4b
[ 0.311162] ? prepare_to_wait_exclusive+0x28/0xb0
[ 0.311164] prepare_to_wait_exclusive+0x28/0xb0
[ 0.311167] wbt_wait+0x127/0x330
[ 0.311169] ? finish_wait+0x80/0x80
[ 0.311172] ? generic_make_request+0xda/0x3b0
[ 0.311174] blk_mq_make_request+0xd6/0x7b0
[ 0.311176] ? blk_queue_enter+0x24/0x260
[ 0.311178] ? generic_make_request+0xda/0x3b0
[ 0.311181] generic_make_request+0x10c/0x3b0
[ 0.311183] ? submit_bio+0x5c/0x110
[ 0.311185] submit_bio+0x5c/0x110
[ 0.311197] ? __ext4_journal_stop+0x36/0xa0 [ext4]
[ 0.311210] ext4_io_submit+0x48/0x60 [ext4]
[ 0.311222] ext4_writepages+0x810/0x11f0 [ext4]
[ 0.311229] ? do_writepages+0x3c/0xd0
[ 0.311239] ? ext4_mark_inode_dirty+0x260/0x260 [ext4]
[ 0.311240] do_writepages+0x3c/0xd0
[ 0.311243] ? _raw_spin_unlock+0x24/0x30
[ 0.311245] ? wbc_attach_and_unlock_inode+0x165/0x280
[ 0.311248] ? __filemap_fdatawrite_range+0xa3/0xe0
[ 0.311250] __filemap_fdatawrite_range+0xa3/0xe0
[ 0.311253] file_write_and_wait_range+0x34/0x90
[ 0.311264] ext4_sync_file+0x151/0x500 [ext4]
[ 0.311267] do_fsync+0x38/0x60
[ 0.311270] SyS_fsync+0xc/0x10
[ 0.311272] do_syscall_64+0x6f/0x170
[ 0.311274] entry_SYSCALL_64_after_hwframe+0x42/0xb7
In the original patch, wbt_done is waking up all the exclusive
processes in the wait queue, which can cause a thundering herd
if there is a large number of writer threads in the queue. The
original intention of the code seems to be to wake up one thread
only however, it uses wake_up_all() in __wbt_done(), and then
uses the following check in __wbt_wait to have only one thread
actually get out of the wait loop:
if (waitqueue_active(&rqw->wait) &&
rqw->wait.head.next != &wait->entry)
return false;
The problem with this is that the wait entry in wbt_wait is
define with DEFINE_WAIT, which uses the autoremove wakeup function.
That means that the above check is invalid - the wait entry will
have been removed from the queue already by the time we hit the
check in the loop.
Secondly, auto-removing the wait entries also means that the wait
queue essentially gets reordered "randomly" (e.g. threads re-add
themselves in the order they got to run after being woken up).
Additionally, new requests entering wbt_wait might overtake requests
that were queued earlier, because the wait queue will be
(temporarily) empty after the wake_up_all, so the waitqueue_active
check will not stop them. This can cause certain threads to starve
under high load.
The fix is to leave the woken up requests in the queue and remove
them in finish_wait() once the current thread breaks out of the
wait loop in __wbt_wait. This will ensure new requests always
end up at the back of the queue, and they won't overtake requests
that are already in the wait queue. With that change, the loop
in wbt_wait is also in line with many other wait loops in the kernel.
Waking up just one thread drastically reduces lock contention, as
does moving the wait queue add/remove out of the loop.
A significant drop in lockdep's lock contention numbers is seen when
running the test application on the patched kernel.
Signed-off-by: Anchal Agarwal <anchalag@amazon.com>
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-08-07 23:40:49 +03:00
__set_current_state ( TASK_RUNNING ) ;
remove_wait_queue ( & rqw - > wait , & wait ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
static inline bool wbt_should_throttle ( struct rq_wb * rwb , struct bio * bio )
{
2018-05-07 19:03:23 +03:00
switch ( bio_op ( bio ) ) {
case REQ_OP_WRITE :
/*
* Don ' t throttle WRITE_ODIRECT
*/
if ( ( bio - > bi_opf & ( REQ_SYNC | REQ_IDLE ) ) = =
( REQ_SYNC | REQ_IDLE ) )
return false ;
/* fallthrough */
case REQ_OP_DISCARD :
return true ;
default :
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
return false ;
2018-05-07 19:03:23 +03:00
}
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
2018-07-03 18:14:59 +03:00
static enum wbt_flags bio_to_wbt_flags ( struct rq_wb * rwb , struct bio * bio )
{
enum wbt_flags flags = 0 ;
2018-08-23 18:34:46 +03:00
if ( ! rwb_enabled ( rwb ) )
return 0 ;
2018-07-03 18:14:59 +03:00
if ( bio_op ( bio ) = = REQ_OP_READ ) {
flags = WBT_READ ;
} else if ( wbt_should_throttle ( rwb , bio ) ) {
if ( current_is_kswapd ( ) )
flags | = WBT_KSWAPD ;
if ( bio_op ( bio ) = = REQ_OP_DISCARD )
flags | = WBT_DISCARD ;
flags | = WBT_TRACKED ;
}
return flags ;
}
static void wbt_cleanup ( struct rq_qos * rqos , struct bio * bio )
{
struct rq_wb * rwb = RQWB ( rqos ) ;
enum wbt_flags flags = bio_to_wbt_flags ( rwb , bio ) ;
__wbt_done ( rqos , flags ) ;
}
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
/*
* Returns true if the IO request should be accounted , false if not .
* May sleep , if we have exceeded the writeback limits . Caller can pass
* in an irq held spinlock , if it holds one when calling this function .
* If we do sleep , we ' ll release and re - grab it .
*/
2018-07-03 18:14:59 +03:00
static void wbt_wait ( struct rq_qos * rqos , struct bio * bio , spinlock_t * lock )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
2018-07-03 18:32:35 +03:00
struct rq_wb * rwb = RQWB ( rqos ) ;
2018-07-03 18:14:59 +03:00
enum wbt_flags flags ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
2018-07-03 18:14:59 +03:00
flags = bio_to_wbt_flags ( rwb , bio ) ;
2018-08-14 18:57:49 +03:00
if ( ! ( flags & WBT_TRACKED ) ) {
2018-07-03 18:14:59 +03:00
if ( flags & WBT_READ )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
wb_timestamp ( rwb , & rwb - > last_issue ) ;
2018-07-03 18:14:59 +03:00
return ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
2018-05-07 18:57:08 +03:00
if ( current_is_kswapd ( ) )
2018-07-03 18:14:59 +03:00
flags | = WBT_KSWAPD ;
2018-05-07 19:03:23 +03:00
if ( bio_op ( bio ) = = REQ_OP_DISCARD )
2018-07-03 18:14:59 +03:00
flags | = WBT_DISCARD ;
2018-05-07 18:57:08 +03:00
2018-07-03 18:14:59 +03:00
__wbt_wait ( rwb , flags , bio - > bi_opf , lock ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
blk-stat: convert to callback-based statistics reporting
Currently, statistics are gathered in ~0.13s windows, and users grab the
statistics whenever they need them. This is not ideal for both in-tree
users:
1. Writeback throttling wants its own dynamically sized window of
statistics. Since the blk-stats statistics are reset after every
window and the wbt windows don't line up with the blk-stats windows,
wbt doesn't see every I/O.
2. Polling currently grabs the statistics on every I/O. Again, depending
on how the window lines up, we may miss some I/Os. It's also
unnecessary overhead to get the statistics on every I/O; the hybrid
polling heuristic would be just as happy with the statistics from the
previous full window.
This reworks the blk-stats infrastructure to be callback-based: users
register a callback that they want called at a given time with all of
the statistics from the window during which the callback was active.
Users can dynamically bucketize the statistics. wbt and polling both
currently use read vs. write, but polling can be extended to further
subdivide based on request size.
The callbacks are kept on an RCU list, and each callback has percpu
stats buffers. There will only be a few users, so the overhead on the
I/O completion side is low. The stats flushing is also simplified
considerably: since the timer function is responsible for clearing the
statistics, we don't have to worry about stale statistics.
wbt is a trivial conversion. After the conversion, the windowing problem
mentioned above is fixed.
For polling, we register an extra callback that caches the previous
window's statistics in the struct request_queue for the hybrid polling
heuristic to use.
Since we no longer have a single stats buffer for the request queue,
this also removes the sysfs and debugfs stats entries. To replace those,
we add a debugfs entry for the poll statistics.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21 18:56:08 +03:00
if ( ! blk_stat_is_active ( rwb - > cb ) )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
rwb_arm_timer ( rwb ) ;
2018-07-03 18:14:59 +03:00
}
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
2018-07-03 18:14:59 +03:00
static void wbt_track ( struct rq_qos * rqos , struct request * rq , struct bio * bio )
{
struct rq_wb * rwb = RQWB ( rqos ) ;
rq - > wbt_flags | = bio_to_wbt_flags ( rwb , bio ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
2018-07-03 18:32:35 +03:00
void wbt_issue ( struct rq_qos * rqos , struct request * rq )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
2018-07-03 18:32:35 +03:00
struct rq_wb * rwb = RQWB ( rqos ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
if ( ! rwb_enabled ( rwb ) )
return ;
/*
2018-05-09 12:08:48 +03:00
* Track sync issue , in case it takes a long time to complete . Allows us
* to react quicker , if a sync IO takes a long time to complete . Note
* that this is just a hint . The request can go away when it completes ,
* so it ' s important we never dereference it . We only use the address to
* compare with , which is why we store the sync_issue time locally .
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
*/
2018-05-09 12:08:48 +03:00
if ( wbt_is_read ( rq ) & & ! rwb - > sync_issue ) {
rwb - > sync_cookie = rq ;
2018-05-09 12:08:50 +03:00
rwb - > sync_issue = rq - > io_start_time_ns ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
}
2018-07-03 18:32:35 +03:00
void wbt_requeue ( struct rq_qos * rqos , struct request * rq )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
2018-07-03 18:32:35 +03:00
struct rq_wb * rwb = RQWB ( rqos ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
if ( ! rwb_enabled ( rwb ) )
return ;
2018-05-09 12:08:48 +03:00
if ( rq = = rwb - > sync_cookie ) {
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
rwb - > sync_issue = 0 ;
rwb - > sync_cookie = NULL ;
}
}
2018-07-03 18:32:35 +03:00
void wbt_set_queue_depth ( struct request_queue * q , unsigned int depth )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
2018-07-03 18:32:35 +03:00
struct rq_qos * rqos = wbt_rq_qos ( q ) ;
if ( rqos ) {
RQWB ( rqos ) - > rq_depth . queue_depth = depth ;
__wbt_update_limits ( RQWB ( rqos ) ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
}
2018-07-03 18:32:35 +03:00
void wbt_set_write_cache ( struct request_queue * q , bool write_cache_on )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
2018-07-03 18:32:35 +03:00
struct rq_qos * rqos = wbt_rq_qos ( q ) ;
if ( rqos )
RQWB ( rqos ) - > wc = write_cache_on ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
}
2017-04-19 12:33:27 +03:00
/*
* Enable wbt if defaults are configured that way
*/
void wbt_enable_default ( struct request_queue * q )
{
2018-07-03 18:32:35 +03:00
struct rq_qos * rqos = wbt_rq_qos ( q ) ;
2017-04-19 12:33:27 +03:00
/* Throttling already enabled? */
2018-07-03 18:32:35 +03:00
if ( rqos )
2017-04-19 12:33:27 +03:00
return ;
/* Queue not registered? Maybe shutting down... */
if ( ! test_bit ( QUEUE_FLAG_REGISTERED , & q - > queue_flags ) )
return ;
if ( ( q - > mq_ops & & IS_ENABLED ( CONFIG_BLK_WBT_MQ ) ) | |
( q - > request_fn & & IS_ENABLED ( CONFIG_BLK_WBT_SQ ) ) )
wbt_init ( q ) ;
}
EXPORT_SYMBOL_GPL ( wbt_enable_default ) ;
2016-11-28 19:22:47 +03:00
u64 wbt_default_latency_nsec ( struct request_queue * q )
{
/*
* We default to 2 msec for non - rotational storage , and 75 msec
* for rotational storage .
*/
if ( blk_queue_nonrot ( q ) )
return 2000000ULL ;
else
return 75000000ULL ;
}
2017-04-21 16:55:42 +03:00
static int wbt_data_dir ( const struct request * rq )
{
2018-02-05 23:16:56 +03:00
const int op = req_op ( rq ) ;
if ( op = = REQ_OP_READ )
return READ ;
2018-05-03 18:14:57 +03:00
else if ( op_is_write ( op ) )
2018-02-05 23:16:56 +03:00
return WRITE ;
/* don't account */
return - 1 ;
2017-04-21 16:55:42 +03:00
}
2018-07-03 18:32:35 +03:00
static void wbt_exit ( struct rq_qos * rqos )
{
struct rq_wb * rwb = RQWB ( rqos ) ;
struct request_queue * q = rqos - > q ;
blk_stat_remove_callback ( q , rwb - > cb ) ;
blk_stat_free_callback ( rwb - > cb ) ;
kfree ( rwb ) ;
}
/*
* Disable wbt , if enabled by default .
*/
void wbt_disable_default ( struct request_queue * q )
{
struct rq_qos * rqos = wbt_rq_qos ( q ) ;
struct rq_wb * rwb ;
if ( ! rqos )
return ;
rwb = RQWB ( rqos ) ;
if ( rwb - > enable_state = = WBT_STATE_ON_DEFAULT )
rwb - > wb_normal = 0 ;
}
EXPORT_SYMBOL_GPL ( wbt_disable_default ) ;
static struct rq_qos_ops wbt_rqos_ops = {
. throttle = wbt_wait ,
. issue = wbt_issue ,
2018-07-03 18:14:59 +03:00
. track = wbt_track ,
2018-07-03 18:32:35 +03:00
. requeue = wbt_requeue ,
. done = wbt_done ,
2018-07-03 18:14:59 +03:00
. cleanup = wbt_cleanup ,
2018-07-03 18:32:35 +03:00
. exit = wbt_exit ,
} ;
2016-11-11 07:50:51 +03:00
int wbt_init ( struct request_queue * q )
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
{
struct rq_wb * rwb ;
int i ;
rwb = kzalloc ( sizeof ( * rwb ) , GFP_KERNEL ) ;
if ( ! rwb )
return - ENOMEM ;
2017-04-21 16:55:42 +03:00
rwb - > cb = blk_stat_alloc_callback ( wb_timer_fn , wbt_data_dir , 2 , rwb ) ;
blk-stat: convert to callback-based statistics reporting
Currently, statistics are gathered in ~0.13s windows, and users grab the
statistics whenever they need them. This is not ideal for both in-tree
users:
1. Writeback throttling wants its own dynamically sized window of
statistics. Since the blk-stats statistics are reset after every
window and the wbt windows don't line up with the blk-stats windows,
wbt doesn't see every I/O.
2. Polling currently grabs the statistics on every I/O. Again, depending
on how the window lines up, we may miss some I/Os. It's also
unnecessary overhead to get the statistics on every I/O; the hybrid
polling heuristic would be just as happy with the statistics from the
previous full window.
This reworks the blk-stats infrastructure to be callback-based: users
register a callback that they want called at a given time with all of
the statistics from the window during which the callback was active.
Users can dynamically bucketize the statistics. wbt and polling both
currently use read vs. write, but polling can be extended to further
subdivide based on request size.
The callbacks are kept on an RCU list, and each callback has percpu
stats buffers. There will only be a few users, so the overhead on the
I/O completion side is low. The stats flushing is also simplified
considerably: since the timer function is responsible for clearing the
statistics, we don't have to worry about stale statistics.
wbt is a trivial conversion. After the conversion, the windowing problem
mentioned above is fixed.
For polling, we register an extra callback that caches the previous
window's statistics in the struct request_queue for the hybrid polling
heuristic to use.
Since we no longer have a single stats buffer for the request queue,
this also removes the sysfs and debugfs stats entries. To replace those,
we add a debugfs entry for the poll statistics.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21 18:56:08 +03:00
if ( ! rwb - > cb ) {
kfree ( rwb ) ;
return - ENOMEM ;
}
2018-07-03 18:32:35 +03:00
for ( i = 0 ; i < WBT_NUM_RWQ ; i + + )
rq_wait_init ( & rwb - > rq_wait [ i ] ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
2018-07-03 18:32:35 +03:00
rwb - > rqos . id = RQ_QOS_WBT ;
rwb - > rqos . ops = & wbt_rqos_ops ;
rwb - > rqos . q = q ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
rwb - > last_comp = rwb - > last_issue = jiffies ;
rwb - > win_nsec = RWB_WINDOW_NSEC ;
2016-11-28 19:40:34 +03:00
rwb - > enable_state = WBT_STATE_ON_DEFAULT ;
2018-07-03 18:32:35 +03:00
rwb - > wc = 1 ;
rwb - > rq_depth . default_depth = RWB_DEF_DEPTH ;
__wbt_update_limits ( rwb ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
/*
blk-stat: convert to callback-based statistics reporting
Currently, statistics are gathered in ~0.13s windows, and users grab the
statistics whenever they need them. This is not ideal for both in-tree
users:
1. Writeback throttling wants its own dynamically sized window of
statistics. Since the blk-stats statistics are reset after every
window and the wbt windows don't line up with the blk-stats windows,
wbt doesn't see every I/O.
2. Polling currently grabs the statistics on every I/O. Again, depending
on how the window lines up, we may miss some I/Os. It's also
unnecessary overhead to get the statistics on every I/O; the hybrid
polling heuristic would be just as happy with the statistics from the
previous full window.
This reworks the blk-stats infrastructure to be callback-based: users
register a callback that they want called at a given time with all of
the statistics from the window during which the callback was active.
Users can dynamically bucketize the statistics. wbt and polling both
currently use read vs. write, but polling can be extended to further
subdivide based on request size.
The callbacks are kept on an RCU list, and each callback has percpu
stats buffers. There will only be a few users, so the overhead on the
I/O completion side is low. The stats flushing is also simplified
considerably: since the timer function is responsible for clearing the
statistics, we don't have to worry about stale statistics.
wbt is a trivial conversion. After the conversion, the windowing problem
mentioned above is fixed.
For polling, we register an extra callback that caches the previous
window's statistics in the struct request_queue for the hybrid polling
heuristic to use.
Since we no longer have a single stats buffer for the request queue,
this also removes the sysfs and debugfs stats entries. To replace those,
we add a debugfs entry for the poll statistics.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21 18:56:08 +03:00
* Assign rwb and add the stats callback .
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
*/
2018-07-03 18:32:35 +03:00
rq_qos_add ( q , & rwb - > rqos ) ;
blk-stat: convert to callback-based statistics reporting
Currently, statistics are gathered in ~0.13s windows, and users grab the
statistics whenever they need them. This is not ideal for both in-tree
users:
1. Writeback throttling wants its own dynamically sized window of
statistics. Since the blk-stats statistics are reset after every
window and the wbt windows don't line up with the blk-stats windows,
wbt doesn't see every I/O.
2. Polling currently grabs the statistics on every I/O. Again, depending
on how the window lines up, we may miss some I/Os. It's also
unnecessary overhead to get the statistics on every I/O; the hybrid
polling heuristic would be just as happy with the statistics from the
previous full window.
This reworks the blk-stats infrastructure to be callback-based: users
register a callback that they want called at a given time with all of
the statistics from the window during which the callback was active.
Users can dynamically bucketize the statistics. wbt and polling both
currently use read vs. write, but polling can be extended to further
subdivide based on request size.
The callbacks are kept on an RCU list, and each callback has percpu
stats buffers. There will only be a few users, so the overhead on the
I/O completion side is low. The stats flushing is also simplified
considerably: since the timer function is responsible for clearing the
statistics, we don't have to worry about stale statistics.
wbt is a trivial conversion. After the conversion, the windowing problem
mentioned above is fixed.
For polling, we register an extra callback that caches the previous
window's statistics in the struct request_queue for the hybrid polling
heuristic to use.
Since we no longer have a single stats buffer for the request queue,
this also removes the sysfs and debugfs stats entries. To replace those,
we add a debugfs entry for the poll statistics.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-03-21 18:56:08 +03:00
blk_stat_add_callback ( q , rwb - > cb ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
2016-11-28 19:22:47 +03:00
rwb - > min_lat_nsec = wbt_default_latency_nsec ( q ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
2018-07-03 18:32:35 +03:00
wbt_set_queue_depth ( q , blk_queue_depth ( q ) ) ;
wbt_set_write_cache ( q , test_bit ( QUEUE_FLAG_WC , & q - > queue_flags ) ) ;
blk-wbt: add general throttling mechanism
We can hook this up to the block layer, to help throttle buffered
writes.
wbt registers a few trace points that can be used to track what is
happening in the system:
wbt_lat: 259:0: latency 2446318
wbt_stat: 259:0: rmean=2446318, rmin=2446318, rmax=2446318, rsamples=1,
wmean=518866, wmin=15522, wmax=5330353, wsamples=57
wbt_step: 259:0: step down: step=1, window=72727272, background=8, normal=16, max=32
This shows a sync issue event (wbt_lat) that exceeded it's time. wbt_stat
dumps the current read/write stats for that window, and wbt_step shows a
step down event where we now scale back writes. Each trace includes the
device, 259:0 in this case.
Signed-off-by: Jens Axboe <axboe@fb.com>
2016-11-09 22:36:15 +03:00
return 0 ;
}