Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210317045949.1584952-1-joshdon@google.com> <20210317082550.GA3881262@gmail.com>
 <CABk29NvGx6KQa_+RU-6xmL6mUeBrqZjH1twOw93SCVD-NZkbMQ@mail.gmail.com> <20210319090252.GF15768@suse.de>
In-Reply-To: <20210319090252.GF15768@suse.de>
From:   Josh Don <joshdon@google.com>
Date:   Mon, 22 Mar 2021 20:35:22 -0700
Message-ID: <CABk29NukHXUu22N5WyVx82TA6WEZsz+HOBmk5oAy4GQMx4W+cw@mail.gmail.com>
Subject: Re: [PATCH] sched: Warn on long periods of pending need_resched
To:     Mel Gorman <mgorman@suse.de>
Cc:     Ingo Molnar <mingo@kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Iurii Zaikin <yzaikin@google.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-fsdevel@vger.kernel.org,
        David Rientjes <rientjes@google.com>,
        Oleg Rombakh <olegrom@google.com>, Paul Turner <pjt@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Mar 19, 2021 at 2:02 AM Mel Gorman <mgorman@suse.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