linux-kernel - Re: Benchmarking [PATCH v5 00/14] SLUB percpu sheaves

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Message-ID: <CAJuCfpHQ_JedSRHKKoYXyVzaFOm=dDWzgFZwqerfEC1fn35j0w@mail.gmail.com>
Date: Wed, 17 Sep 2025 09:14:37 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Uladzislau Rezki <urezki@...il.com>
Cc: Vlastimil Babka <vbabka@...e.cz>, paulmck@...nel.org, Jan Engelhardt <ej@...i.de>, 
	Sudarsan Mahendran <sudarsanm@...gle.com>, Liam.Howlett@...cle.com, cl@...two.org, 
	harry.yoo@...cle.com, howlett@...il.com, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, maple-tree@...ts.infradead.org, rcu@...r.kernel.org, 
	rientjes@...gle.com, roman.gushchin@...ux.dev
Subject: Re: Benchmarking [PATCH v5 00/14] SLUB percpu sheaves

On Tue, Sep 16, 2025 at 10:19 PM Uladzislau Rezki <urezki@...il.com> wrote:
>
> On Tue, Sep 16, 2025 at 10:09:18AM -0700, Suren Baghdasaryan wrote:
> > On Mon, Sep 15, 2025 at 8:22 AM Vlastimil Babka <vbabka@...e.cz> wrote:
> > >
> > > On 9/15/25 14:13, Paul E. McKenney wrote:
> > > > On Mon, Sep 15, 2025 at 09:51:25AM +0200, Jan Engelhardt wrote:
> > > >>
> > > >> On Saturday 2025-09-13 02:09, Sudarsan Mahendran wrote:
> > > >> >
> > > >> >Summary of the results:
> > >
> > > In any case, thanks a lot for the results!
> > >
> > > >> >- Significant change (meaning >10% difference
> > > >> >  between base and experiment) on will-it-scale
> > > >> >  tests in AMD.
> > > >> >
> > > >> >Summary of AMD will-it-scale test changes:
> > > >> >
> > > >> >Number of runs : 15
> > > >> >Direction      : + is good
> > > >>
> > > >> If STDDEV grows more than mean, there is more jitter,
> > > >> which is not "good".
> > > >
> > > > This is true.  On the other hand, the mean grew way more in absolute
> > > > terms than did STDDEV.  So might this be a reasonable tradeoff?
> > >
> > > Also I'd point out that MIN of TEST is better than MAX of BASE, which means
> > > there's always an improvement for this config. So jitter here means it's
> > > changing between better and more better :) and not between worse and (more)
> > > better.
> > >
> > > The annoying part of course is that for other configs it's consistently the
> > > opposite.
> >
> > Hi Vlastimil,
> > I ran my mmap stress test that runs 20000 cycles of mmapping 50 VMAs,
> > faulting them in then unmapping and timing only mmap and munmap calls.
> > This is not a realistic scenario but works well for A/B comparison.
> >
> > The numbers are below with sheaves showing a clear improvement:
> >
> > Baseline
> >             avg             stdev
> > mmap        2.621073        0.2525161631
> > munmap      2.292965        0.008831973052
> > total       4.914038        0.2572620923
> >
> > Sheaves
> >             avg            stdev           avg_diff        stdev_diff
> > mmap        1.561220667    0.07748897037   -40.44%        -69.31%
> > munmap      2.042071       0.03603083448   -10.94%        307.96%
> > total       3.603291667    0.113209047     -26.67%        -55.99%
> >
> Could you run your test with dropping below patch?

Sure, will try later today and report.

>
> [PATCH v8 04/23] slab: add sheaf support for batching kfree_rcu() operations
>
> mmap()/munmap(), i assume it is a duration time in average, is the time
> in microseconds?

Yeah, it ends up being in microseconds. The actual reported time is
the total time in seconds that all mmap/munmap in the test consumed.
With 20000 cycles of 50 mmap/munmap calls we end up with 1000000
syscalls, so the number can be considered as duration in microseconds
for a single call.

>
> Thank you.
>
> --
> Uladzislau Rezki