linux-kernel - Re: [fanotify] a8b98c808e: stress-ng.fanotify.ops_per

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Date:   Thu, 3 Jun 2021 09:57:15 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     kernel test robot <oliver.sang@...el.com>
Cc:     Jan Kara <jack@...e.cz>, Matthew Bobrowski <repnop@...gle.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        kbuild test robot <lkp@...el.com>, ying.huang@...el.com,
        feng.tang@...el.com, zhengjun.xing@...ux.intel.com,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [fanotify] a8b98c808e: stress-ng.fanotify.ops_per_sec 32.2% improvement

On Thu, Jun 3, 2021 at 4:36 AM kernel test robot <oliver.sang@...el.com> wrote:
>
>
>
> Greeting,
>
> FYI, we noticed a 32.2% improvement of stress-ng.fanotify.ops_per_sec due to commit:
>
>
> commit: a8b98c808eab3ec8f1b5a64be967b0f4af4cae43 ("fanotify: fix permission model of unprivileged group")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>
>

I guess now we know what caused the reported regression:
https://lore.kernel.org/lkml/20210511124632.GL24154@quack2.suse.cz/

I didn't know that capable() is so significant.

FWIW, here is a link to the test code:
https://github.com/ColinIanKing/stress-ng/blob/master/stress-fanotify.c#L474

It creates events in a loop by child process while the parent process
reads the generated events in a loop (on two different fanotify groups).

Thanks,
Amir.