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block, bfq: replace mechanism for evaluating I/O intensity

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Some BFQ mechanisms make their decisions on a bfq_queue basing also on
whether the bfq_queue is I/O bound. In this respect, the current logic
for evaluating whether a bfq_queue is I/O bound is rather rough. This
commits replaces this logic with a more effective one.

The new logic measures the percentage of time during which a bfq_queue
is active, and marks the bfq_queue as I/O bound if the latter if this
percentage is above a fixed threshold.

Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Paolo Valente 2021-01-25 20:02:43 +01:00 committed by Jens Axboe
parent 3a905c37c3
commit eb2fd80f9d
2 changed files with 52 additions and 27 deletions
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63
block/bfq-iosched.c
View File

@ -1026,6 +1026,8 @@ bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
bfqq->entity.new_weight = bic->saved_weight;
bfqq->ttime = bic->saved_ttime;
bfqq->io_start_time = bic->saved_io_start_time;
bfqq->tot_idle_time = bic->saved_tot_idle_time;
bfqq->wr_coeff = bic->saved_wr_coeff;
bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
@ -1721,17 +1723,6 @@ static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
bfq_clear_bfqq_just_created(bfqq);
if (!bfq_bfqq_IO_bound(bfqq)) {
if (arrived_in_time) {
bfqq->requests_within_timer++;
if (bfqq->requests_within_timer >=
bfqd->bfq_requests_within_timer)
bfq_mark_bfqq_IO_bound(bfqq);
} else
bfqq->requests_within_timer = 0;
}
if (bfqd->low_latency) {
if (unlikely(time_is_after_jiffies(bfqq->split_time)))
/* wraparound */
@ -1865,6 +1856,36 @@ static void bfq_reset_inject_limit(struct bfq_data *bfqd,
bfqq->decrease_time_jif = jiffies;
}
static void bfq_update_io_intensity(struct bfq_queue *bfqq, u64 now_ns)
{
u64 tot_io_time = now_ns - bfqq->io_start_time;
if (RB_EMPTY_ROOT(&bfqq->sort_list) && bfqq->dispatched == 0)
bfqq->tot_idle_time +=
now_ns - bfqq->ttime.last_end_request;
if (unlikely(bfq_bfqq_just_created(bfqq)))
return;
/*
* Must be busy for at least about 80% of the time to be
* considered I/O bound.
*/
if (bfqq->tot_idle_time * 5 > tot_io_time)
bfq_clear_bfqq_IO_bound(bfqq);
else
bfq_mark_bfqq_IO_bound(bfqq);
/*
* Keep an observation window of at most 200 ms in the past
* from now.
*/
if (tot_io_time > 200 * NSEC_PER_MSEC) {
bfqq->io_start_time = now_ns - (tot_io_time>>1);
bfqq->tot_idle_time >>= 1;
}
}
static void bfq_add_request(struct request *rq)
{
struct bfq_queue *bfqq = RQ_BFQQ(rq);
@ -1872,6 +1893,7 @@ static void bfq_add_request(struct request *rq)
struct request *next_rq, *prev;
unsigned int old_wr_coeff = bfqq->wr_coeff;
bool interactive = false;
u64 now_ns = ktime_get_ns();
bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
bfqq->queued[rq_is_sync(rq)]++;
@ -1934,7 +1956,7 @@ static void bfq_add_request(struct request *rq)
*/
if (bfqd->last_completed_rq_bfqq &&
!bfq_bfqq_has_short_ttime(bfqq) &&
ktime_get_ns() - bfqd->last_completion <
now_ns - bfqd->last_completion <
4 * NSEC_PER_MSEC) {
if (bfqd->last_completed_rq_bfqq != bfqq &&
bfqd->last_completed_rq_bfqq !=
@ -2051,6 +2073,9 @@ static void bfq_add_request(struct request *rq)
}
}
if (bfq_bfqq_sync(bfqq))
bfq_update_io_intensity(bfqq, now_ns);
elv_rb_add(&bfqq->sort_list, rq);
/*
@ -2712,6 +2737,8 @@ static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
bic->saved_ttime = bfqq->ttime;
bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
bic->saved_io_start_time = bfqq->io_start_time;
bic->saved_tot_idle_time = bfqq->tot_idle_time;
bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
if (unlikely(bfq_bfqq_just_created(bfqq) &&
@ -3979,10 +4006,6 @@ void bfq_bfqq_expire(struct bfq_data *bfqd,
bfq_bfqq_budget_left(bfqq) >= entity->budget / 3)))
bfq_bfqq_charge_time(bfqd, bfqq, delta);
if (reason == BFQQE_TOO_IDLE &&
entity->service <= 2 * entity->budget / 10)
bfq_clear_bfqq_IO_bound(bfqq);
if (bfqd->low_latency && bfqq->wr_coeff == 1)
bfqq->last_wr_start_finish = jiffies;
@ -5085,6 +5108,8 @@ static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
struct bfq_io_cq *bic, pid_t pid, int is_sync)
{
u64 now_ns = ktime_get_ns();
RB_CLEAR_NODE(&bfqq->entity.rb_node);
INIT_LIST_HEAD(&bfqq->fifo);
INIT_HLIST_NODE(&bfqq->burst_list_node);
@ -5112,7 +5137,9 @@ static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
bfq_clear_bfqq_sync(bfqq);
/* set end request to minus infinity from now */
bfqq->ttime.last_end_request = ktime_get_ns() + 1;
bfqq->ttime.last_end_request = now_ns + 1;
bfqq->io_start_time = now_ns;
bfq_mark_bfqq_IO_bound(bfqq);
@ -6524,8 +6551,6 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
bfqd->bfq_slice_idle = bfq_slice_idle;
bfqd->bfq_timeout = bfq_timeout;
bfqd->bfq_requests_within_timer = 120;
bfqd->bfq_large_burst_thresh = 8;
bfqd->bfq_burst_interval = msecs_to_jiffies(180);

16
block/bfq-iosched.h
View File

@ -291,6 +291,11 @@ struct bfq_queue {
/* associated @bfq_ttime struct */
struct bfq_ttime ttime;
/* when bfqq started to do I/O within the last observation window */
u64 io_start_time;
/* how long bfqq has remained empty during the last observ. window */
u64 tot_idle_time;
/* bit vector: a 1 for each seeky requests in history */
u32 seek_history;
@ -407,6 +412,9 @@ struct bfq_io_cq {
*/
bool saved_IO_bound;
u64 saved_io_start_time;
u64 saved_tot_idle_time;
/*
* Same purpose as the previous fields for the value of the
* field keeping the queue's belonging to a large burst
@ -641,14 +649,6 @@ struct bfq_data {
*/
unsigned int bfq_timeout;
/*
* Number of consecutive requests that must be issued within
* the idle time slice to set again idling to a queue which
* was marked as non-I/O-bound (see the definition of the
* IO_bound flag for further details).
*/
unsigned int bfq_requests_within_timer;
/*
* Force device idling whenever needed to provide accurate
* service guarantees, without caring about throughput