On Tue, Aug 06 2019, Jinpu Wang wrote:
> On Tue, Aug 6, 2019 at 9:54 AM Jinpu Wang <jinpu.wang@xxxxxxxxxxxxxxx> wrote:
>>
>> On Tue, Aug 6, 2019 at 1:46 AM NeilBrown <neilb@xxxxxxxx> wrote:
>> >
>> > On Mon, Aug 05 2019, Jinpu Wang wrote:
>> >
>> > > Hi Neil,
>> > >
>> > > For the md higher write IO latency problem, I bisected it to these commits:
>> > >
>> > > 4ad23a97 MD: use per-cpu counter for writes_pending
>> > > 210f7cd percpu-refcount: support synchronous switch to atomic mode.
>> > >
>> > > Do you maybe have an idea? How can we fix it?
>> >
>> > Hmmm.... not sure.
>> Hi Neil,
>>
>> Thanks for reply, detailed result in line.
Thanks for the extra testing.
...
> [ 105.133299] md md0 in_sync is 0, sb_flags 2, recovery 3, external
> 0, safemode 0, recovery_cp 524288
...
ahh - the resync was still happening. That explains why set_in_sync()
is being called so often. If you wait for sync to complete (or create
the array with --assume-clean) you should see more normal behaviour.
This patch should fix it. I think we can do better but it would be more
complex so no suitable for backports to -stable.
Once you confirm it works, I'll send it upstream with a
Reported-and-Tested-by from you.
Thanks,
NeilBrown
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 24638ccedce4..624cf1ac43dc 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8900,6 +8900,7 @@ 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;
@@ -8945,7 +8946,7 @@ 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);
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