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

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Message-ID: <aMpE-oSjtlDU4TSl@pc636>
Date: Wed, 17 Sep 2025 07:19:54 +0200
From: Uladzislau Rezki <urezki@...il.com>
To: Suren Baghdasaryan <surenb@...gle.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, urezki@...il.com
Subject: Re: Benchmarking [PATCH v5 00/14] SLUB percpu sheaves

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?

[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?

Thank you. 

--
Uladzislau Rezki