From: Roman Gushchin <guro@fb.com>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: Josef Bacik <josef@toxicpanda.com>,
Thorsten Leemhuis <regressions@leemhuis.info>,
<peterz@infradead.org>, <vincent.guittot@linaro.org>,
<torvalds@linux-foundation.org>, <linux-kernel@vger.kernel.org>,
<linux-btrfs@vger.kernel.org>, <clm@fb.com>
Subject: Re: [REGRESSION] 5-10% increase in IO latencies with nohz balance patch
Date: Thu, 13 Jan 2022 08:57:18 -0800 [thread overview]
Message-ID: <YeBZ7qNjPsonEYZz@carbon.dhcp.thefacebook.com> (raw)
In-Reply-To: <87k0f37fl6.mognet@arm.com>
On Thu, Jan 13, 2022 at 04:41:57PM +0000, Valentin Schneider wrote:
> On 03/01/22 11:16, Josef Bacik wrote:
> > On Wed, Dec 22, 2021 at 04:07:35PM +0000, Valentin Schneider wrote:
> >>
> >> Hi,
> >>
> >> On 22/12/21 13:42, Thorsten Leemhuis wrote:
> >> > What's the status here? Just wondering, because there hasn't been any
> >> > activity in this thread since 11 days and the festive season is upon us.
> >> >
> >> > Was the discussion moved elsewhere? Or is this still a mystery? And if
> >> > it is: how bad is it, does it need to be fixed before Linus releases 5.16?
> >> >
> >>
> >> I got to the end of bisect #3 yesterday, the incriminated commit doesn't
> >> seem to make much sense but I've just re-tested it and there is a clear
> >> regression between that commit and its parent (unlike bisect #1 and #2):
> >>
> >> 2127d22509aec3a83dffb2a3c736df7ba747a7ce mm, slub: fix two bugs in slab_debug_trace_open()
> >> write_clat_ns_p99 195395.92 199638.20 4797.01 2.17%
> >> write_iops 17305.79 17188.24 250.66 -0.68%
> >>
> >> write_clat_ns_p99 195543.84 199996.70 5122.88 2.28%
> >> write_iops 17300.61 17241.86 251.56 -0.34%
> >>
> >> write_clat_ns_p99 195543.84 200724.48 5122.88 2.65%
> >> write_iops 17300.61 17246.63 251.56 -0.31%
> >>
> >> write_clat_ns_p99 195543.84 200445.41 5122.88 2.51%
> >> write_iops 17300.61 17215.47 251.56 -0.49%
> >>
> >> 6d2aec9e123bb9c49cb5c7fc654f25f81e688e8c mm/mempolicy: do not allow illegal MPOL_F_NUMA_BALANCING | MPOL_LOCAL in mbind()
> >> write_clat_ns_p99 195395.92 197942.30 4797.01 1.30%
> >> write_iops 17305.79 17246.56 250.66 -0.34%
> >>
> >> write_clat_ns_p99 195543.84 196183.92 5122.88 0.33%
> >> write_iops 17300.61 17310.33 251.56 0.06%
> >>
> >> write_clat_ns_p99 195543.84 196990.71 5122.88 0.74%
> >> write_iops 17300.61 17346.32 251.56 0.26%
> >>
> >> write_clat_ns_p99 195543.84 196362.24 5122.88 0.42%
> >> write_iops 17300.61 17315.71 251.56 0.09%
> >>
> >> It's pure debug stuff and AFAICT is a correct fix...
> >> @Josef, could you test that on your side?
> >
> > Sorry, holidays and all that. I see 0 difference between the two commits, and
> > no regression from baseline. It'll take me a few days to recover from the
> > holidays, but I'll put some more effort into actively debugging wtf is going on
> > here on my side since we're all having trouble pinning down what's going
> > on.
>
> Humph, that's unfortunate... I just came back from my holidays, so I'll be
> untangling my inbox for the next few days. Do keep us posted!
I'm trying to bisect it independently and make sense of it too, thanks to Josef
for providing me a test setup. From the very first data I've got yesterday,
the only thing I can say the data is very noisy and I'm not totally convinced
that the regression is coming from the patch which was blamed initially.
I hope to make more progress today/tomorrow, will keep you updated.
Thanks!
next prev parent reply other threads:[~2022-01-13 16:57 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-29 17:03 [REGRESSION] 5-10% increase in IO latencies with nohz balance patch Josef Bacik
2021-11-29 18:03 ` Valentin Schneider
2021-11-29 18:15 ` Josef Bacik
2021-11-29 18:31 ` Valentin Schneider
2021-11-29 19:49 ` Josef Bacik
2021-11-30 0:26 ` Valentin Schneider
2021-12-03 12:03 ` Valentin Schneider
2021-12-03 19:00 ` Josef Bacik
2021-12-06 9:48 ` Valentin Schneider
2021-12-09 17:22 ` Valentin Schneider
2021-12-09 19:16 ` Josef Bacik
2021-12-22 12:42 ` Thorsten Leemhuis
2021-12-22 16:07 ` Valentin Schneider
2022-01-03 16:16 ` Josef Bacik
2022-01-13 16:41 ` Valentin Schneider
2022-01-13 16:57 ` Roman Gushchin [this message]
2022-02-18 11:00 ` Thorsten Leemhuis
2022-02-18 15:34 ` Josef Bacik
2021-11-30 7:16 ` Thorsten Leemhuis
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