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authorNeilBrown2019-08-20 10:21:09 +1000
committerSong Liu2019-08-27 12:36:36 -0700
commit480523feae581ab714ba6610388a3b4619a2f695 (patch)
tree6d9a364a68f5a7ae8c19a76b58080161d2bbd48d
parent97b27821b4854ca744946dae32a3f2fd55bcd5bc (diff)
md: only call set_in_sync() when it is expected to succeed.
Since commit 4ad23a976413 ("MD: use per-cpu counter for writes_pending"), set_in_sync() is substantially more expensive: it can wait for a full RCU grace period which can be 10s of milliseconds. So we should only call it when the cost is justified. md_check_recovery() currently calls set_in_sync() every time it finds anything to do (on non-external active arrays). For an array performing resync or recovery, this will be quite often. Each call will introduce a delay to the md thread, which can noticeable affect IO submission latency. In md_check_recovery() we only need to call set_in_sync() if 'safemode' was non-zero at entry, meaning that there has been not recent IO. So we save this "safemode was nonzero" state, and only call set_in_sync() if it was non-zero. This measurably reduces mean and maximum IO submission latency during resync/recovery. Reported-and-tested-by: Jack Wang <jinpu.wang@cloud.ionos.com> Fixes: 4ad23a976413 ("MD: use per-cpu counter for writes_pending") Cc: stable@vger.kernel.org (v4.12+) Signed-off-by: NeilBrown <neilb@suse.com> Signed-off-by: Song Liu <songliubraving@fb.com>
-rw-r--r--drivers/md/md.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/md/md.c b/drivers/md/md.c
index daa885ee4d60..21efb0b949a6 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8932,6 +8932,7 @@ void md_check_recovery(struct mddev *mddev)
if (mddev_trylock(mddev)) {
int spares = 0;
+ bool try_set_sync = mddev->safemode != 0;
if (!mddev->external && mddev->safemode == 1)
mddev->safemode = 0;
@@ -8977,7 +8978,7 @@ void md_check_recovery(struct mddev *mddev)
}
}
- if (!mddev->external && !mddev->in_sync) {
+ if (try_set_sync && !mddev->external && !mddev->in_sync) {
spin_lock(&mddev->lock);
set_in_sync(mddev);
spin_unlock(&mddev->lock);