linux-kernel - Re: [x86/signal] 3aac3ebea0: will-it-scale.per_thread

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Date:   Tue, 07 Dec 2021 21:36:31 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Bae, Chang Seok" <chang.seok.bae@...el.com>
Cc:     "Sang, Oliver" <oliver.sang@...el.com>,
        Borislav Petkov <bp@...e.de>,
        LKML <linux-kernel@...r.kernel.org>,
        "lkp@...ts.01.org" <lkp@...ts.01.org>, lkp <lkp@...el.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Tang, Feng" <feng.tang@...el.com>,
        "zhengjun.xing@...ux.intel.com" <zhengjun.xing@...ux.intel.com>,
        "Yin, Fengwei" <fengwei.yin@...el.com>
Subject: Re: [x86/signal]  3aac3ebea0:  will-it-scale.per_thread_ops -11.9%
 regression

On Tue, Dec 07 2021 at 18:49, Chang Seok Bae wrote:
> On Dec 7, 2021, at 05:38, Thomas Gleixner <tglx@...utronix.de> wrote:
>> On Tue, Dec 07 2021 at 09:21, kernel test robot wrote:
>>> (please be noted we made some further analysis before reporting out,
>>> and thought it's likely the regression is related with the extra spinlock
>>> introducded by enalbling DYNAMIC_SIGFRAME. below is the full report.)
>>> 
>>> FYI, we noticed a -11.9% regression of will-it-scale.per_thread_ops due to commit:
>> 
>> Does that use sigaltstack() ?
>
> FWIW, I was also wondering about this with:
>
> $ git clone https://github.com/antonblanchard/will-it-scale.git
> $ cd will-it-scale/
> $ git grep sigaltstack
> $
>
> But, the test seems to use python via runtest.py. And the python code has
> sigaltstack():
>     https://github.com/python/cpython/blob/main/Modules/faulthandler.c#L454

But how does that affect the test written in C? Mysterious!