On Wed, Aug 7, 2019 at 1:40 AM NeilBrown <neilb@xxxxxxxx> wrote:
>
> 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.
I've updated my tests accordingly, thanks for the hint.
>
> 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
Thanks a lot, Neil, my quick test show, yes, it fixed the problem for me.
I will run more tests to be sure, will report back the test result.
Regards,
Jack Wang
>
>
> 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);
