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bcache: New writeback PD controller

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The old writeback PD controller could get into states where it had throttled all
the way down and take way too long to recover - it was too complicated to really
understand what it was doing.

This rewrites a good chunk of it to hopefully be simpler and make more sense,
and it also pays more attention to units which should make the behaviour a bit
easier to understand.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
This commit is contained in:
Kent Overstreet 2013-11-11 13:58:34 -08:00
parent 6d3d1a9c54
commit 16749c23c0
4 changed files with 62 additions and 49 deletions
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6
drivers/md/bcache/bcache.h
View File

@ -373,14 +373,14 @@ struct cached_dev {
unsigned char writeback_percent;
unsigned writeback_delay;
int writeback_rate_change;
int64_t writeback_rate_derivative;
uint64_t writeback_rate_target;
int64_t writeback_rate_proportional;
int64_t writeback_rate_derivative;
int64_t writeback_rate_change;
unsigned writeback_rate_update_seconds;
unsigned writeback_rate_d_term;
unsigned writeback_rate_p_term_inverse;
unsigned writeback_rate_d_smooth;
};
enum alloc_watermarks {

50
drivers/md/bcache/sysfs.c
View File

@ -83,7 +83,6 @@ rw_attribute(writeback_rate);
rw_attribute(writeback_rate_update_seconds);
rw_attribute(writeback_rate_d_term);
rw_attribute(writeback_rate_p_term_inverse);
rw_attribute(writeback_rate_d_smooth);
read_attribute(writeback_rate_debug);
read_attribute(stripe_size);
@ -129,31 +128,41 @@ SHOW(__bch_cached_dev)
var_printf(writeback_running, "%i");
var_print(writeback_delay);
var_print(writeback_percent);
sysfs_print(writeback_rate, dc->writeback_rate.rate);
sysfs_hprint(writeback_rate, dc->writeback_rate.rate << 9);
var_print(writeback_rate_update_seconds);
var_print(writeback_rate_d_term);
var_print(writeback_rate_p_term_inverse);
var_print(writeback_rate_d_smooth);
if (attr == &sysfs_writeback_rate_debug) {
char rate[20];
char dirty[20];
char derivative[20];
char target[20];
bch_hprint(dirty,
bcache_dev_sectors_dirty(&dc->disk) << 9);
bch_hprint(derivative, dc->writeback_rate_derivative << 9);
char proportional[20];
char derivative[20];
char change[20];
s64 next_io;
bch_hprint(rate, dc->writeback_rate.rate << 9);
bch_hprint(dirty, bcache_dev_sectors_dirty(&dc->disk) << 9);
bch_hprint(target, dc->writeback_rate_target << 9);
bch_hprint(proportional,dc->writeback_rate_proportional << 9);
bch_hprint(derivative, dc->writeback_rate_derivative << 9);
bch_hprint(change, dc->writeback_rate_change << 9);
next_io = div64_s64(dc->writeback_rate.next - local_clock(),
NSEC_PER_MSEC);
return sprintf(buf,
"rate:\t\t%u\n"
"change:\t\t%i\n"
"rate:\t\t%s/sec\n"
"dirty:\t\t%s\n"
"target:\t\t%s\n"
"proportional:\t%s\n"
"derivative:\t%s\n"
"target:\t\t%s\n",
dc->writeback_rate.rate,
dc->writeback_rate_change,
dirty, derivative, target);
"change:\t\t%s/sec\n"
"next io:\t%llims\n",
rate, dirty, target, proportional,
derivative, change, next_io);
}
sysfs_hprint(dirty_data,
@ -189,6 +198,7 @@ STORE(__cached_dev)
struct kobj_uevent_env *env;
#define d_strtoul(var) sysfs_strtoul(var, dc->var)
#define d_strtoul_nonzero(var) sysfs_strtoul_clamp(var, dc->var, 1, INT_MAX)
#define d_strtoi_h(var) sysfs_hatoi(var, dc->var)
sysfs_strtoul(data_csum, dc->disk.data_csum);
@ -197,16 +207,15 @@ STORE(__cached_dev)
d_strtoul(writeback_metadata);
d_strtoul(writeback_running);
d_strtoul(writeback_delay);
sysfs_strtoul_clamp(writeback_rate,
dc->writeback_rate.rate, 1, 1000000);
sysfs_strtoul_clamp(writeback_percent, dc->writeback_percent, 0, 40);
d_strtoul(writeback_rate_update_seconds);
sysfs_strtoul_clamp(writeback_rate,
dc->writeback_rate.rate, 1, INT_MAX);
d_strtoul_nonzero(writeback_rate_update_seconds);
d_strtoul(writeback_rate_d_term);
d_strtoul(writeback_rate_p_term_inverse);
sysfs_strtoul_clamp(writeback_rate_p_term_inverse,
dc->writeback_rate_p_term_inverse, 1, INT_MAX);
d_strtoul(writeback_rate_d_smooth);
d_strtoul_nonzero(writeback_rate_p_term_inverse);
d_strtoi_h(sequential_cutoff);
d_strtoi_h(readahead);
@ -313,7 +322,6 @@ static struct attribute *bch_cached_dev_files[] = {
&sysfs_writeback_rate_update_seconds,
&sysfs_writeback_rate_d_term,
&sysfs_writeback_rate_p_term_inverse,
&sysfs_writeback_rate_d_smooth,
&sysfs_writeback_rate_debug,
&sysfs_dirty_data,
&sysfs_stripe_size,

8
drivers/md/bcache/util.c
View File

@ -209,7 +209,13 @@ uint64_t bch_next_delay(struct bch_ratelimit *d, uint64_t done)
{
uint64_t now = local_clock();
d->next += div_u64(done, d->rate);
d->next += div_u64(done * NSEC_PER_SEC, d->rate);
if (time_before64(now + NSEC_PER_SEC, d->next))
d->next = now + NSEC_PER_SEC;
if (time_after64(now - NSEC_PER_SEC * 2, d->next))
d->next = now - NSEC_PER_SEC * 2;
return time_after64(d->next, now)
? div_u64(d->next - now, NSEC_PER_SEC / HZ)

47
drivers/md/bcache/writeback.c
View File

@ -30,38 +30,40 @@ static void __update_writeback_rate(struct cached_dev *dc)
/* PD controller */
int change = 0;
int64_t error;
int64_t dirty = bcache_dev_sectors_dirty(&dc->disk);
int64_t derivative = dirty - dc->disk.sectors_dirty_last;
int64_t proportional = dirty - target;
int64_t change;
dc->disk.sectors_dirty_last = dirty;
derivative *= dc->writeback_rate_d_term;
derivative = clamp(derivative, -dirty, dirty);
/* Scale to sectors per second */
proportional *= dc->writeback_rate_update_seconds;
proportional = div_s64(proportional, dc->writeback_rate_p_term_inverse);
derivative = div_s64(derivative, dc->writeback_rate_update_seconds);
derivative = ewma_add(dc->disk.sectors_dirty_derivative, derivative,
dc->writeback_rate_d_smooth, 0);
(dc->writeback_rate_d_term /
dc->writeback_rate_update_seconds) ?: 1, 0);
/* Avoid divide by zero */
if (!target)
goto out;
derivative *= dc->writeback_rate_d_term;
derivative = div_s64(derivative, dc->writeback_rate_p_term_inverse);
error = div64_s64((dirty + derivative - target) << 8, target);
change = div_s64((dc->writeback_rate.rate * error) >> 8,
dc->writeback_rate_p_term_inverse);
change = proportional + derivative;
/* Don't increase writeback rate if the device isn't keeping up */
if (change > 0 &&
time_after64(local_clock(),
dc->writeback_rate.next + 10 * NSEC_PER_MSEC))
dc->writeback_rate.next + NSEC_PER_MSEC))
change = 0;
dc->writeback_rate.rate =
clamp_t(int64_t, dc->writeback_rate.rate + change,
clamp_t(int64_t, (int64_t) dc->writeback_rate.rate + change,
1, NSEC_PER_MSEC);
out:
dc->writeback_rate_proportional = proportional;
dc->writeback_rate_derivative = derivative;
dc->writeback_rate_change = change;
dc->writeback_rate_target = target;
@ -87,15 +89,11 @@ static void update_writeback_rate(struct work_struct *work)
static unsigned writeback_delay(struct cached_dev *dc, unsigned sectors)
{
uint64_t ret;
if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
!dc->writeback_percent)
return 0;
ret = bch_next_delay(&dc->writeback_rate, sectors * 10000000ULL);
return min_t(uint64_t, ret, HZ);
return bch_next_delay(&dc->writeback_rate, sectors);
}
struct dirty_io {
@ -476,6 +474,8 @@ void bch_sectors_dirty_init(struct cached_dev *dc)
bch_btree_map_keys(&op.op, dc->disk.c, &KEY(op.inode, 0, 0),
sectors_dirty_init_fn, 0);
dc->disk.sectors_dirty_last = bcache_dev_sectors_dirty(&dc->disk);
}
int bch_cached_dev_writeback_init(struct cached_dev *dc)
@ -490,10 +490,9 @@ int bch_cached_dev_writeback_init(struct cached_dev *dc)
dc->writeback_delay = 30;
dc->writeback_rate.rate = 1024;
dc->writeback_rate_update_seconds = 30;
dc->writeback_rate_d_term = 16;
dc->writeback_rate_p_term_inverse = 64;
dc->writeback_rate_d_smooth = 8;
dc->writeback_rate_update_seconds = 5;
dc->writeback_rate_d_term = 30;
dc->writeback_rate_p_term_inverse = 6000;
dc->writeback_thread = kthread_create(bch_writeback_thread, dc,
"bcache_writeback");