linux-kernel - Re: [perf/x86/amd] 471af006a7: will-it-scale.per_process

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Date:   Wed, 12 Feb 2020 13:18:30 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kernel test robot <rong.a.chen@...el.com>
Cc:     Kim Phillips <kim.phillips@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        lkp@...ts.01.org
Subject: Re: [perf/x86/amd] 471af006a7: will-it-scale.per_process_ops -7.6%
 regression

On Wed, Feb 12, 2020 at 07:35:14PM +0800, kernel test robot wrote:
> Greeting,
> 
> FYI, we noticed a -7.6% regression of will-it-scale.per_process_ops due to commit:
> 
> 
> commit: 471af006a747f1c535c8a8c6c0973c320fe01b22 ("perf/x86/amd: Constrain Large Increment per Cycle events")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> in testcase: will-it-scale
> on test machine: 88 threads Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz with 128G memory

That commit only changes code relevant to AMD machines; give you have
this result on an Intel machine makes me think the bisect is flawed.