linux-kernel - Re: [PCI/MSI] 77e89afc25: will-it-scale.per_process

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Date:   Fri, 27 Aug 2021 00:32:26 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     kernel report robot <oliver.sang@...el.com>
Cc:     Marc Zyngier <maz@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        lkp@...ts.01.org, lkp@...el.com, ying.huang@...el.com,
        feng.tang@...el.com, zhengjun.xing@...ux.intel.com
Subject: Re: [PCI/MSI]  77e89afc25:  will-it-scale.per_process_ops -2.6%
 regression

On Wed, Aug 18 2021 at 22:51, kernel report robot wrote:

> Greeting,
>
> FYI, we noticed a -2.6% regression of will-it-scale.per_process_ops due to commit:
>
>
> commit: 77e89afc25f30abd56e76a809ee2884d7c1b63ce ("PCI/MSI: Protect msi_desc::masked for multi-MSI")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>
>
> in testcase: will-it-scale
> on test machine: 128 threads 2 sockets Intel(R) Xeon(R) Gold 6338 CPU @ 2.00GHz with 256G memory
> with following parameters:
>
> 	nr_task: 100%
> 	mode: process
> 	test: lseek2
> 	cpufreq_governor: performance
> 	ucode: 0xd000280
>
> test-description: Will It Scale takes a testcase and runs it from 1 through to n parallel copies to see if the testcase will scale. It builds both a process and threads based test in order to see any differences between the two.
> test-url: https://github.com/antonblanchard/will-it-scale
>
> If you fix the issue, kindly add following tag
> Reported-by: kernel test robot <oliver.sang@...el.com>

There is nothing to fix. The commit cures an incorrectness. Comparing
buggy code to correct code is futile.

Thanks,

        tglx