linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Josh Don <joshdon@google.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: 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>, Mel Gorman <mgorman@suse.de>,
	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>
Subject: Re: [PATCH] sched: Warn on long periods of pending need_resched
Date: Wed, 17 Mar 2021 17:06:31 -0700	[thread overview]
Message-ID: <CABk29NvGx6KQa_+RU-6xmL6mUeBrqZjH1twOw93SCVD-NZkbMQ@mail.gmail.com> (raw)
In-Reply-To: <20210317082550.GA3881262@gmail.com>

On Wed, Mar 17, 2021 at 1:25 AM Ingo Molnar <mingo@kernel.org> wrote:
>
> * Josh Don <joshdon@google.com> wrote:
>
> > If resched_latency_warn_ms is set to the default value, only one warning
> > will be produced per boot.
>
> Looks like a value hack, should probably be a separate flag,
> defaulting to warn-once.

Agreed, done.

> > This warning only exists under CONFIG_SCHED_DEBUG. If it goes off, it is
> > likely that there is a missing cond_resched() somewhere.
>
> CONFIG_SCHED_DEBUG is default-y, so most distros have it enabled.

To avoid log spam for people who don't care, I was considering having
the feature default disabled. Perhaps a better alternative is to only
show a single line warning and not print the full backtrace by
default. Does the latter sound good to you?

> > +#ifdef CONFIG_KASAN
> > +#define RESCHED_DEFAULT_WARN_LATENCY_MS 101
> > +#define RESCHED_BOOT_QUIET_SEC 600
> > +#else
> > +#define RESCHED_DEFAULT_WARN_LATENCY_MS 51
> > +#define RESCHED_BOOT_QUIET_SEC 300
> >  #endif
> > +int sysctl_resched_latency_warn_ms = RESCHED_DEFAULT_WARN_LATENCY_MS;
> > +#endif /* CONFIG_SCHED_DEBUG */
>
> I'd really just make this a single value - say 100 or 200 msecs.

Replacing these both with a single value (the more conservative
default of 100ms and 600s).

> > +static inline void resched_latency_warn(int cpu, u64 latency)
> > +{
> > +     static DEFINE_RATELIMIT_STATE(latency_check_ratelimit, 60 * 60 * HZ, 1);
> > +
> > +     WARN(__ratelimit(&latency_check_ratelimit),
> > +          "CPU %d: need_resched set for > %llu ns (%d ticks) "
> > +          "without schedule\n",
> > +          cpu, latency, cpu_rq(cpu)->ticks_without_resched);
> > +}
>
> Could you please put the 'sched:' prefix into scheduler warnings.
> Let's have a bit of a namespace structure in new warnings.

Sounds good, done.

  reply	other threads:[~2021-03-18  0:07 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-17  4:59 [PATCH] sched: Warn on long periods of pending need_resched Josh Don
2021-03-17  8:25 ` Ingo Molnar
2021-03-18  0:06   ` Josh Don [this message]
2021-03-19  9:02     ` Mel Gorman
2021-03-23  3:35       ` Josh Don
2021-03-17  8:31 ` Ingo Molnar
2021-03-18  0:17   ` Josh Don
2021-03-18 14:31 ` [sched] 663017c554: WARNING:at_kernel/sched/core.c:#scheduler_tick kernel test robot
2021-03-18 20:41   ` Josh Don

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CABk29NvGx6KQa_+RU-6xmL6mUeBrqZjH1twOw93SCVD-NZkbMQ@mail.gmail.com \
    --to=joshdon@google.com \
    --cc=bristot@redhat.com \
    --cc=bsegall@google.com \
    --cc=dietmar.eggemann@arm.com \
    --cc=juri.lelli@redhat.com \
    --cc=keescook@chromium.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mcgrof@kernel.org \
    --cc=mgorman@suse.de \
    --cc=mingo@kernel.org \
    --cc=mingo@redhat.com \
    --cc=olegrom@google.com \
    --cc=peterz@infradead.org \
    --cc=pjt@google.com \
    --cc=rientjes@google.com \
    --cc=rostedt@goodmis.org \
    --cc=vincent.guittot@linaro.org \
    --cc=yzaikin@google.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).