linux-kernel - Re: [fsnotify] c738fbabb0: will-it-scale.per_process

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Date:   Sun, 26 Jul 2020 14:52:47 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Rong Chen <rong.a.chen@...el.com>
Cc:     Jan Kara <jack@...e.cz>, LKML <linux-kernel@...r.kernel.org>,
        lkp@...ts.01.org
Subject: Re: [fsnotify] c738fbabb0: will-it-scale.per_process_ops -9.5% regression

On Fri, Jul 24, 2020 at 6:47 AM Amir Goldstein <amir73il@...il.com> wrote:
>
> On Fri, Jul 24, 2020 at 5:45 AM Rong Chen <rong.a.chen@...el.com> wrote:
> >
> >
> >
> > On 7/21/20 11:59 PM, Amir Goldstein wrote:
> > > On Tue, Jul 21, 2020 at 3:15 AM kernel test robot <rong.a.chen@...el.com> wrote:
> > >> Greeting,
> > >>
> > >> FYI, we noticed a -9.5% regression of will-it-scale.per_process_ops due to commit:
> > >>
> > >>
> > >> commit: c738fbabb0ff62d0f9a9572e56e65d05a1b34c6a ("fsnotify: fold fsnotify() call into fsnotify_parent()")
> > > Strange, that's a pretty dumb patch moving some inlined code from one
> > > function to
> > > another (assuming there are no fsnotify marks in this test).
> > >
> > > Unless I am missing something the only thing that changes slightly is
> > > an extra d_inode(file->f_path.dentry) deference.
> > > I can get rid of it.
> > >
> > > Is it possible to ask for a re-test with fix patch (attached)?
> >
> > Hi Amir,
> >
> > We failed to apply this patch, could you tell us the base commit or the
> > base branch?
> >
>
> Hi Rong,
>
> The patch is applied on top of the reported offending commit:
> c738fbabb0ff62d0f9a9572e56e65d05a1b34c6a ("fsnotify: fold fsnotify()
> call into fsnotify_parent()")
>
> I pushed it to my github:
> https://github.com/amir73il/linux/commits/for_lkp
>

FWIW, I tried reproducing the reported regression on a local machine.

I ran the test twice on each of the branch commits:

26dc3d2bff62 fsnotify: pass inode to fsnotify_parent()
c738fbabb0ff fsnotify: fold fsnotify() call into fsnotify_parent()
71d734103edf fsnotify: Rearrange fast path to minimise overhead when
there is no watcher
47aaabdedf36 fanotify: Avoid softlockups when reading many events

Not only did I not observe a regression with the reported commit,
but there was a slight improvement. And then there yet was another
improvement with the fix commit on top of it.

But it could be that I am doing something wrong, because I have zero
millage with LKP.

=========================================================================================
compiler/cpufreq_governor/kconfig/mode/nr_task/rootfs/tbox_group/test/testcase:
  gcc-7/performance/defconfig/process/16/ubuntu/amir-lkp/open1/will-it-scale

commit:
  47aaabdedf366ac5894c7fddec388832f0d8193e
  71d734103edfa2b4c6657578a3082ee0e51d767e
  c738fbabb0ff62d0f9a9572e56e65d05a1b34c6a
  26dc3d2bff623768cbbd0c8053ddd6390fd828d2

47aaabdedf366ac5 71d734103edfa2b4c6657578a30
c738fbabb0ff62d0f9a9572e56e 26dc3d2bff623768cbbd0c8053d
---------------- ---------------------------
--------------------------- ---------------------------
       fail:runs  %reproduction    fail:runs  %reproduction
fail:runs  %reproduction    fail:runs
           |             |             |             |             |
          |             |
         45:2         -555%          34:2         -807%          29:2
       -996%          25:2     dmesg.timestamp:last
         45:2         -555%          34:2         -807%          29:2
       -996%          25:2     kmsg.timestamp:last
         %stddev     %change         %stddev     %change
%stddev     %change         %stddev
             \          |                \          |                \
         |                \
   1097404            +1.7%    1116452            +2.7%    1126533
       +3.5%    1135663        will-it-scale.16.processes
      0.02 ± 60%     +20.0%       0.03 ± 66%     +20.0%       0.03 ±
66%     -20.0%       0.02 ± 50%  will-it-scale.16.processes_idle
     68587            +1.7%      69778            +2.7%      70408
       +3.5%      70978        will-it-scale.per_process_ops


Thanks,
Amir.