From: NeilBrown neilb@suse.com
Currently if many flush requests are submitted to an md device is quick succession, they are serialized and can take a long to process them all. We don't really need to call flush all those times - a single flush call can satisfy all requests submitted before it started. So keep track of when the current flush started and when it finished, allow any pending flush that was requested before the flush started to complete without waiting any more.
Test results from Xiao:
Test is done on a raid10 device which is created by 4 SSDs. The tool is dbench.
1. The latest linux stable kernel Operation Count AvgLat MaxLat -------------------------------------------------- Deltree 768 10.509 78.305 Flush 2078376 0.013 10.094 Close 21787697 0.019 18.821 LockX 96580 0.007 3.184 Mkdir 384 0.008 0.062 Rename 1255883 0.191 23.534 ReadX 46495589 0.020 14.230 WriteX 14790591 7.123 60.706 Unlink 5989118 0.440 54.551 UnlockX 96580 0.005 2.736 FIND_FIRST 10393845 0.042 12.079 SET_FILE_INFORMATION 2415558 0.129 10.088 QUERY_FILE_INFORMATION 4711725 0.005 8.462 QUERY_PATH_INFORMATION 26883327 0.032 21.715 QUERY_FS_INFORMATION 4929409 0.010 8.238 NTCreateX 29660080 0.100 53.268
Throughput 1034.88 MB/sec (sync open) 128 clients 128 procs max_latency=60.712 ms
2. With patch1 "Revert "MD: fix lock contention for flush bios"" Operation Count AvgLat MaxLat -------------------------------------------------- Deltree 256 8.326 36.761 Flush 693291 3.974 180.269 Close 7266404 0.009 36.929 LockX 32160 0.006 0.840 Mkdir 128 0.008 0.021 Rename 418755 0.063 29.945 ReadX 15498708 0.007 7.216 WriteX 4932310 22.482 267.928 Unlink 1997557 0.109 47.553 UnlockX 32160 0.004 1.110 FIND_FIRST 3465791 0.036 7.320 SET_FILE_INFORMATION 805825 0.015 1.561 QUERY_FILE_INFORMATION 1570950 0.005 2.403 QUERY_PATH_INFORMATION 8965483 0.013 14.277 QUERY_FS_INFORMATION 1643626 0.009 3.314 NTCreateX 9892174 0.061 41.278
Throughput 345.009 MB/sec (sync open) 128 clients 128 procs max_latency=267.939 m
3. With patch1 and patch2 Operation Count AvgLat MaxLat -------------------------------------------------- Deltree 768 9.570 54.588 Flush 2061354 0.666 15.102 Close 21604811 0.012 25.697 LockX 95770 0.007 1.424 Mkdir 384 0.008 0.053 Rename 1245411 0.096 12.263 ReadX 46103198 0.011 12.116 WriteX 14667988 7.375 60.069 Unlink 5938936 0.173 30.905 UnlockX 95770 0.005 4.147 FIND_FIRST 10306407 0.041 11.715 SET_FILE_INFORMATION 2395987 0.048 7.640 QUERY_FILE_INFORMATION 4672371 0.005 9.291 QUERY_PATH_INFORMATION 26656735 0.018 19.719 QUERY_FS_INFORMATION 4887940 0.010 7.654 NTCreateX 29410811 0.059 28.551
Throughput 1026.21 MB/sec (sync open) 128 clients 128 procs max_latency=60.075 ms
Cc: stable@vger.kernel.org # v4.19+ Tested-by: Xiao Ni xni@redhat.com Signed-off-by: NeilBrown neilb@suse.com Signed-off-by: Song Liu songliubraving@fb.com --- drivers/md/md.c | 27 +++++++++++++++++++++++---- drivers/md/md.h | 3 +++ 2 files changed, 26 insertions(+), 4 deletions(-)
diff --git a/drivers/md/md.c b/drivers/md/md.c index 021e522001c1..d0f688399a56 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -427,6 +427,7 @@ static void submit_flushes(struct work_struct *ws) struct mddev *mddev = container_of(ws, struct mddev, flush_work); struct md_rdev *rdev;
+ mddev->start_flush = ktime_get_boottime(); INIT_WORK(&mddev->flush_work, md_submit_flush_data); atomic_set(&mddev->flush_pending, 1); rcu_read_lock(); @@ -467,6 +468,7 @@ static void md_submit_flush_data(struct work_struct *ws) * could wait for this and below md_handle_request could wait for those * bios because of suspend check */ + mddev->last_flush = mddev->start_flush; mddev->flush_bio = NULL; wake_up(&mddev->sb_wait);
@@ -481,15 +483,32 @@ static void md_submit_flush_data(struct work_struct *ws)
void md_flush_request(struct mddev *mddev, struct bio *bio) { + ktime_t start = ktime_get_boottime(); spin_lock_irq(&mddev->lock); wait_event_lock_irq(mddev->sb_wait, - !mddev->flush_bio, + !mddev->flush_bio || + ktime_after(mddev->last_flush, start), mddev->lock); - mddev->flush_bio = bio; + if (!ktime_after(mddev->last_flush, start)) { + WARN_ON(mddev->flush_bio); + mddev->flush_bio = bio; + bio = NULL; + } spin_unlock_irq(&mddev->lock);
- INIT_WORK(&mddev->flush_work, submit_flushes); - queue_work(md_wq, &mddev->flush_work); + if (!bio) { + INIT_WORK(&mddev->flush_work, submit_flushes); + queue_work(md_wq, &mddev->flush_work); + } else { + /* flush was performed for some other bio while we waited. */ + if (bio->bi_iter.bi_size == 0) + /* an empty barrier - all done */ + bio_endio(bio); + else { + bio->bi_opf &= ~REQ_PREFLUSH; + mddev->pers->make_request(mddev, bio); + } + } } EXPORT_SYMBOL(md_flush_request);
diff --git a/drivers/md/md.h b/drivers/md/md.h index 2deb84fa93f9..257cb4c9e22b 100644 --- a/drivers/md/md.h +++ b/drivers/md/md.h @@ -463,6 +463,9 @@ struct mddev { */ struct bio *flush_bio; atomic_t flush_pending; + ktime_t start_flush, last_flush; /* last_flush is when the last completed + * flush was started. + */ struct work_struct flush_work; struct work_struct event_work; /* used by dm to report failure event */ void (*sync_super)(struct mddev *mddev, struct md_rdev *rdev);