Re: [fsnotify] 4c40d6efc8: unixbench.score -3.3% regression

[Jan Kara]

On Sun 01-08-21 09:32:40, Amir Goldstein wrote:
> On Sat, Jul 31, 2021 at 10:51 PM Gabriel Krisman Bertazi
> <krisman@xxxxxxxxxxxxx> wrote:
> >
> > Amir Goldstein <amir73il@xxxxxxxxx> writes:
> >
> > > On Sat, Jul 31, 2021 at 9:20 AM kernel test robot <oliver.sang@xxxxxxxxx> wrote:
> > >>
> > >>
> > >>
> > >> Greeting,
> > >>
> > >> FYI, we noticed a -3.3% regression of unixbench.score due to commit:
> > >>
> > >>
> > >> commit: 4c40d6efc8b22b88a45c335ffd6d25b55d769f5b ("[PATCH v4 08/16] fsnotify: pass arguments of fsnotify() in struct fsnotify_event_info")
> > >> url: https://github.com/0day-ci/linux/commits/Gabriel-Krisman-Bertazi/File-system-wide-monitoring/20210721-001444
> > >> base: https://git.kernel.org/cgit/linux/kernel/git/jack/linux-fs.git fsnotify
> > >>
> > >> in testcase: unixbench
> > >> on test machine: 96 threads 2 sockets Intel(R) Xeon(R) CPU @ 2.30GHz with 128G memory
> > >> with following parameters:
> > >>
> > >>         runtime: 300s
> > >>         nr_task: 1
> > >>         test: pipe
> > >>         cpufreq_governor: performance
> > >>         ucode: 0x4003006
> > >>
> > >> test-description: UnixBench is the original BYTE UNIX benchmark suite aims to test performance of Unix-like system.
> > >> test-url: https://github.com/kdlucas/byte-unixbench
> > >>
> > >> In addition to that, the commit also has significant impact on the following tests:
> > >>
> > >> +------------------+-------------------------------------------------------------------------------------+
> > >> | testcase: change | will-it-scale: will-it-scale.per_thread_ops -1.3% regression                        |
> > >> | test machine     | 192 threads 4 sockets Intel(R) Xeon(R) Platinum 9242 CPU @ 2.30GHz with 192G memory |
> > >> | test parameters  | cpufreq_governor=performance                                                        |
> > >> |                  | mode=thread                                                                         |
> > >> |                  | nr_task=100%                                                                        |
> > >> |                  | test=eventfd1                                                                       |
> > >> |                  | ucode=0x5003006                                                                     |
> > >> +------------------+-------------------------------------------------------------------------------------+
> > >>
> > >>
> > >> If you fix the issue, kindly add following tag
> > >> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> > >>
> > >
> > > Gabriel,
> > >
> > > It looks like my change throws away much of the performance gain for
> > > small IO on pipes without any watches that was achieved by commit
> > > 71d734103edf ("fsnotify: Rearrange fast path to minimise overhead
> > > when there is no watcher").
> > >
> > > I think the way to fix it is to lift the optimization in __fsnotify()
> > > to the fsnotify_parent() inline wrapper as Mel considered doing
> > > but was not sure it was worth the effort at the time.
> > >
> > > It's not completely trivial. I think it requires setting a flag
> > > MNT_FSNOTIFY_WATCHED when there are watches on the
> > > vfsmount. I will look into it.
> >
> > Amir,
> >
> > Since this patch is a clean up, would you mind if I drop it from my
> > series and base my work on top of mainline? Eventually, we can rebase
> > this patch, when the performance issue is addressed.
> >
> > I ask because I'm about to send a v5 and I'm not sure if I should wait
> > to have this fixed.
> 
> I guess you mean that you want to add the sb to fsnotify() args list.
> I don't mind, it's up to Jan.

Yeah, no problem with that from my side either.

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR