linux-kernel - Re: [PATCH] sched: Warn on long periods of pending need

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Message-ID: <CABk29NukHXUu22N5WyVx82TA6WEZsz+HOBmk5oAy4GQMx4W+cw@mail.gmail.com>
Date:   Mon, 22 Mar 2021 20:35:22 -0700
From:   Josh Don <joshdon@...gle.com>
To:     Mel Gorman <mgorman@...e.de>
Cc:     Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org,
        David Rientjes <rientjes@...gle.com>,
        Oleg Rombakh <olegrom@...gle.com>, Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH] sched: Warn on long periods of pending need_resched

On Fri, Mar 19, 2021 at 2:02 AM Mel Gorman <mgorman@...e.de> wrote:
>
> Default disabling and hidden behind a static branch would be useful
> because the majority of users are not going to know what to do about
> a need_resched warning and the sysctl is not documented. As Ingo said,
> SCHED_DEBUG is enabled by default a lot. While I'm not sure what motivates
> most distributions, I have found it useful to display topology information
> on boot and in rare cases, for the enabling/disabling of sched features.
> Hence, sched debug features should avoid adding too much overhead where
> possible.
>
> The static branch would mean splitting the very large inline functions
> adding by the patch. The inline section should do a static check only and
> do the main work in a function in kernel/sched/debug.c so it has minimal
> overhead if unused.
>
> --
> Mel Gorman
> SUSE Labs

Makes sense, I'll include this in v2.

Thanks,
Josh