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

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Message-ID: <d1ef1cbb-c18d-4da6-b56b-342e86dca525@suse.cz>
Date: Mon, 15 Sep 2025 17:22:14 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: paulmck@...nel.org, Jan Engelhardt <ej@...i.de>
Cc: 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, surenb@...gle.com, urezki@...il.com
Subject: Re: Benchmarking [PATCH v5 00/14] SLUB percpu sheaves

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.

> Of course, if adjustments can be made to keep the increase in mean while
> keeping STDDEV low, that would of course be even better.
> 
> 							Thanx, Paul
> 
>> >|            | MIN        | MAX        | MEAN       | MEDIAN     | STDDEV     |
>> >|:-----------|:-----------|:-----------|:-----------|:-----------|:-----------|
>> >| brk1_8_processes
>> >| BASE       | 7,667,220  | 7,705,767  | 7,682,782  | 7,676,211  | 12,733     |
>> >| TEST       | 9,477,395  | 10,053,058 | 9,878,753  | 9,959,360  | 182,014    |
>> >| %          | +23.61%    | +30.46%    | +28.58%    | +29.74%    | +1,329.46% |
>> >
>> >| mmap2_256_processes
>> >| BASE       | 7,483,929  | 7,532,461  | 7,491,876  | 7,489,398  | 11,134     |
>> >| TEST       | 11,580,023 | 16,508,551 | 15,337,145 | 15,943,608 | 1,489,489  |
>> >| %          | +54.73%    | +119.17%   | +104.72%   | +112.88%   | +13,276.75%|
>>