From: dongdong tao dongdong.tao@canonical.com
mainline inclusion from v5.12-rc1 commit 71dda2a5625f31bc3410cb69c3d31376a2b66f28 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I59A5L?from=project-issue CVE: N/A
Current way to calculate the writeback rate only considered the dirty sectors, this usually works fine when the fragmentation is not high, but it will give us unreasonable small rate when we are under a situation that very few dirty sectors consumed a lot dirty buckets. In some case, the dirty bucekts can reached to CUTOFF_WRITEBACK_SYNC while the dirty data(sectors) not even reached the writeback_percent, the writeback rate will still be the minimum value (4k), thus it will cause all the writes to be stucked in a non-writeback mode because of the slow writeback.
We accelerate the rate in 3 stages with different aggressiveness, the first stage starts when dirty buckets percent reach above BCH_WRITEBACK_FRAGMENT_THRESHOLD_LOW (50), the second is BCH_WRITEBACK_FRAGMENT_THRESHOLD_MID (57), the third is BCH_WRITEBACK_FRAGMENT_THRESHOLD_HIGH (64). By default the first stage tries to writeback the amount of dirty data in one bucket (on average) in (1 / (dirty_buckets_percent - 50)) second, the second stage tries to writeback the amount of dirty data in one bucket in (1 / (dirty_buckets_percent - 57)) * 100 millisecond, the third stage tries to writeback the amount of dirty data in one bucket in (1 / (dirty_buckets_percent - 64)) millisecond.
the initial rate at each stage can be controlled by 3 configurable parameters writeback_rate_fp_term_{low|mid|high}, they are by default 1, 10, 1000, the hint of IO throughput that these values are trying to achieve is described by above paragraph, the reason that I choose those value as default is based on the testing and the production data, below is some details:
A. When it comes to the low stage, there is still a bit far from the 70 threshold, so we only want to give it a little bit push by setting the term to 1, it means the initial rate will be 170 if the fragment is 6, it is calculated by bucket_size/fragment, this rate is very small, but still much reasonable than the minimum 8. For a production bcache with unheavy workload, if the cache device is bigger than 1 TB, it may take hours to consume 1% buckets, so it is very possible to reclaim enough dirty buckets in this stage, thus to avoid entering the next stage.
B. If the dirty buckets ratio didn't turn around during the first stage, it comes to the mid stage, then it is necessary for mid stage to be more aggressive than low stage, so i choose the initial rate to be 10 times more than low stage, that means 1700 as the initial rate if the fragment is 6. This is some normal rate we usually see for a normal workload when writeback happens because of writeback_percent.
C. If the dirty buckets ratio didn't turn around during the low and mid stages, it comes to the third stage, and it is the last chance that we can turn around to avoid the horrible cutoff writeback sync issue, then we choose 100 times more aggressive than the mid stage, that means 170000 as the initial rate if the fragment is 6. This is also inferred from a production bcache, I've got one week's writeback rate data from a production bcache which has quite heavy workloads, again, the writeback is triggered by the writeback percent, the highest rate area is around 100000 to 240000, so I believe this kind aggressiveness at this stage is reasonable for production. And it should be mostly enough because the hint is trying to reclaim 1000 bucket per second, and from that heavy production env, it is consuming 50 bucket per second on average in one week's data.
Option writeback_consider_fragment is to control whether we want this feature to be on or off, it's on by default.
Lastly, below is the performance data for all the testing result, including the data from production env: https://docs.google.com/document/d/1AmbIEa_2MhB9bqhC3rfga9tp7n9YX9PLn0jSUxsc...
Signed-off-by: dongdong tao dongdong.tao@canonical.com Signed-off-by: Coly Li colyli@suse.de Signed-off-by: Jens Axboe axboe@kernel.dk --- drivers/md/bcache/bcache.h | 4 ++++ drivers/md/bcache/sysfs.c | 23 +++++++++++++++++++ drivers/md/bcache/writeback.c | 42 +++++++++++++++++++++++++++++++++++ drivers/md/bcache/writeback.h | 4 ++++ 4 files changed, 73 insertions(+)
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h index e8bf4f752e8b..848dd4db1659 100644 --- a/drivers/md/bcache/bcache.h +++ b/drivers/md/bcache/bcache.h @@ -373,6 +373,7 @@ struct cached_dev { unsigned int partial_stripes_expensive:1; unsigned int writeback_metadata:1; unsigned int writeback_running:1; + unsigned int writeback_consider_fragment:1; unsigned char writeback_percent; unsigned int writeback_delay;
@@ -385,6 +386,9 @@ struct cached_dev { unsigned int writeback_rate_update_seconds; unsigned int writeback_rate_i_term_inverse; unsigned int writeback_rate_p_term_inverse; + unsigned int writeback_rate_fp_term_low; + unsigned int writeback_rate_fp_term_mid; + unsigned int writeback_rate_fp_term_high; unsigned int writeback_rate_minimum;
enum stop_on_failure stop_when_cache_set_failed; diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c index 00a520c03f41..eef15f8022ba 100644 --- a/drivers/md/bcache/sysfs.c +++ b/drivers/md/bcache/sysfs.c @@ -117,10 +117,14 @@ rw_attribute(writeback_running); rw_attribute(writeback_percent); rw_attribute(writeback_delay); rw_attribute(writeback_rate); +rw_attribute(writeback_consider_fragment);
rw_attribute(writeback_rate_update_seconds); rw_attribute(writeback_rate_i_term_inverse); rw_attribute(writeback_rate_p_term_inverse); +rw_attribute(writeback_rate_fp_term_low); +rw_attribute(writeback_rate_fp_term_mid); +rw_attribute(writeback_rate_fp_term_high); rw_attribute(writeback_rate_minimum); read_attribute(writeback_rate_debug);
@@ -195,6 +199,7 @@ SHOW(__bch_cached_dev) var_printf(bypass_torture_test, "%i"); var_printf(writeback_metadata, "%i"); var_printf(writeback_running, "%i"); + var_printf(writeback_consider_fragment, "%i"); var_print(writeback_delay); var_print(writeback_percent); sysfs_hprint(writeback_rate, @@ -205,6 +210,9 @@ SHOW(__bch_cached_dev) var_print(writeback_rate_update_seconds); var_print(writeback_rate_i_term_inverse); var_print(writeback_rate_p_term_inverse); + var_print(writeback_rate_fp_term_low); + var_print(writeback_rate_fp_term_mid); + var_print(writeback_rate_fp_term_high); var_print(writeback_rate_minimum);
if (attr == &sysfs_writeback_rate_debug) { @@ -303,6 +311,7 @@ STORE(__cached_dev) sysfs_strtoul_bool(bypass_torture_test, dc->bypass_torture_test); sysfs_strtoul_bool(writeback_metadata, dc->writeback_metadata); sysfs_strtoul_bool(writeback_running, dc->writeback_running); + sysfs_strtoul_bool(writeback_consider_fragment, dc->writeback_consider_fragment); sysfs_strtoul_clamp(writeback_delay, dc->writeback_delay, 0, UINT_MAX);
sysfs_strtoul_clamp(writeback_percent, dc->writeback_percent, @@ -331,6 +340,16 @@ STORE(__cached_dev) sysfs_strtoul_clamp(writeback_rate_p_term_inverse, dc->writeback_rate_p_term_inverse, 1, UINT_MAX); + sysfs_strtoul_clamp(writeback_rate_fp_term_low, + dc->writeback_rate_fp_term_low, + 1, dc->writeback_rate_fp_term_mid - 1); + sysfs_strtoul_clamp(writeback_rate_fp_term_mid, + dc->writeback_rate_fp_term_mid, + dc->writeback_rate_fp_term_low + 1, + dc->writeback_rate_fp_term_high - 1); + sysfs_strtoul_clamp(writeback_rate_fp_term_high, + dc->writeback_rate_fp_term_high, + dc->writeback_rate_fp_term_mid + 1, UINT_MAX); sysfs_strtoul_clamp(writeback_rate_minimum, dc->writeback_rate_minimum, 1, UINT_MAX); @@ -499,9 +518,13 @@ static struct attribute *bch_cached_dev_files[] = { &sysfs_writeback_delay, &sysfs_writeback_percent, &sysfs_writeback_rate, + &sysfs_writeback_consider_fragment, &sysfs_writeback_rate_update_seconds, &sysfs_writeback_rate_i_term_inverse, &sysfs_writeback_rate_p_term_inverse, + &sysfs_writeback_rate_fp_term_low, + &sysfs_writeback_rate_fp_term_mid, + &sysfs_writeback_rate_fp_term_high, &sysfs_writeback_rate_minimum, &sysfs_writeback_rate_debug, &sysfs_io_errors, diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index a129e4d2707c..82d4e0880a99 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -88,6 +88,44 @@ static void __update_writeback_rate(struct cached_dev *dc) int64_t integral_scaled; uint32_t new_rate;
+ /* + * We need to consider the number of dirty buckets as well + * when calculating the proportional_scaled, Otherwise we might + * have an unreasonable small writeback rate at a highly fragmented situation + * when very few dirty sectors consumed a lot dirty buckets, the + * worst case is when dirty buckets reached cutoff_writeback_sync and + * dirty data is still not even reached to writeback percent, so the rate + * still will be at the minimum value, which will cause the write + * stuck at a non-writeback mode. + */ + struct cache_set *c = dc->disk.c; + + int64_t dirty_buckets = c->nbuckets - c->avail_nbuckets; + + if (dc->writeback_consider_fragment && + c->gc_stats.in_use > BCH_WRITEBACK_FRAGMENT_THRESHOLD_LOW && dirty > 0) { + int64_t fragment = + div_s64((dirty_buckets * c->cache->sb.bucket_size), dirty); + int64_t fp_term; + int64_t fps; + + if (c->gc_stats.in_use <= BCH_WRITEBACK_FRAGMENT_THRESHOLD_MID) { + fp_term = dc->writeback_rate_fp_term_low * + (c->gc_stats.in_use - BCH_WRITEBACK_FRAGMENT_THRESHOLD_LOW); + } else if (c->gc_stats.in_use <= BCH_WRITEBACK_FRAGMENT_THRESHOLD_HIGH) { + fp_term = dc->writeback_rate_fp_term_mid * + (c->gc_stats.in_use - BCH_WRITEBACK_FRAGMENT_THRESHOLD_MID); + } else { + fp_term = dc->writeback_rate_fp_term_high * + (c->gc_stats.in_use - BCH_WRITEBACK_FRAGMENT_THRESHOLD_HIGH); + } + fps = div_s64(dirty, dirty_buckets) * fp_term; + if (fragment > 3 && fps > proportional_scaled) { + /* Only overrite the p when fragment > 3 */ + proportional_scaled = fps; + } + } + if ((error < 0 && dc->writeback_rate_integral > 0) || (error > 0 && time_before64(local_clock(), dc->writeback_rate.next + NSEC_PER_MSEC))) { @@ -977,6 +1015,7 @@ void bch_cached_dev_writeback_init(struct cached_dev *dc)
dc->writeback_metadata = true; dc->writeback_running = false; + dc->writeback_consider_fragment = true; dc->writeback_percent = 10; dc->writeback_delay = 30; atomic_long_set(&dc->writeback_rate.rate, 1024); @@ -984,6 +1023,9 @@ void bch_cached_dev_writeback_init(struct cached_dev *dc)
dc->writeback_rate_update_seconds = WRITEBACK_RATE_UPDATE_SECS_DEFAULT; dc->writeback_rate_p_term_inverse = 40; + dc->writeback_rate_fp_term_low = 1; + dc->writeback_rate_fp_term_mid = 10; + dc->writeback_rate_fp_term_high = 1000; dc->writeback_rate_i_term_inverse = 10000;
WARN_ON(test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags)); diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h index 3f1230e22de0..02b2f9df73f6 100644 --- a/drivers/md/bcache/writeback.h +++ b/drivers/md/bcache/writeback.h @@ -16,6 +16,10 @@
#define BCH_AUTO_GC_DIRTY_THRESHOLD 50
+#define BCH_WRITEBACK_FRAGMENT_THRESHOLD_LOW 50 +#define BCH_WRITEBACK_FRAGMENT_THRESHOLD_MID 57 +#define BCH_WRITEBACK_FRAGMENT_THRESHOLD_HIGH 64 + #define BCH_DIRTY_INIT_THRD_MAX 64 /* * 14 (16384ths) is chosen here as something that each backing device