From 16749c23c00c686ed168471963e3ddb0f3fcd855 Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Mon, 11 Nov 2013 13:58:34 -0800 Subject: [PATCH] bcache: New writeback PD controller 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 --- drivers/md/bcache/bcache.h | 6 ++--- drivers/md/bcache/sysfs.c | 50 ++++++++++++++++++++--------------- drivers/md/bcache/util.c | 8 +++++- drivers/md/bcache/writeback.c | 47 ++++++++++++++++---------------- 4 files changed, 62 insertions(+), 49 deletions(-) diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h index a7b1a7631ed2..754f43177483 100644 --- a/drivers/md/bcache/bcache.h +++ b/drivers/md/bcache/bcache.h @@ -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 { diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c index 80d4c2bee18a..a1f85612f0b3 100644 --- a/drivers/md/bcache/sysfs.c +++ b/drivers/md/bcache/sysfs.c @@ -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, diff --git a/drivers/md/bcache/util.c b/drivers/md/bcache/util.c index 462214eeacbe..bb37618e7664 100644 --- a/drivers/md/bcache/util.c +++ b/drivers/md/bcache/util.c @@ -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) diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 3cd931d3f26c..6c44fe059c27 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -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");