From: Thomas Gleixner <tglx@linutronix.de>
To: Ani Sinha <ani@anisinha.ca>, linux-kernel@vger.kernel.org
Cc: anirban.sinha@nokia.com, Ani Sinha <ani@anisinha.ca>,
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>,
Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH v3] Add kernel logs when sched clock unstable and NO_HZ_FULL is not possible
Date: Tue, 22 Jun 2021 17:14:48 +0200 [thread overview]
Message-ID: <87r1gudj87.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210620101312.1757363-1-ani@anisinha.ca>
On Sun, Jun 20 2021 at 15:43, Ani Sinha wrote:
> Commit 4f49b90abb4aca ("sched-clock: Migrate to use new tick
> dependency mask model") had also removed the kernel warning
> message informing the user that it was not possible to turn
> on NO_HZ_FULL. Adding back that log message here. It is
> unhelpful when the kernel turns off NO_HZ_FULL silently
> without informing anyone.
> Also added a kernel log when sched clock is marked as unstable.
Don't do two things at once. See Documentation/process/....
Also your subject line want's a proper prefix.
> diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
> index c2b2859ddd82..9f9fe658f8a5 100644
> --- a/kernel/sched/clock.c
> +++ b/kernel/sched/clock.c
> @@ -192,8 +192,11 @@ void clear_sched_clock_stable(void)
>
> smp_mb(); /* matches sched_clock_init_late() */
>
> - if (static_key_count(&sched_clock_running.key) == 2)
> + if (static_key_count(&sched_clock_running.key) == 2) {
> + WARN_ONCE(sched_clock_stable(),
> + "sched clock is now marked unstable.");
What's the WARN for here? That backtrace is largely uninteresting.
> - if (can_stop_full_tick(cpu, ts))
> + if (can_stop_full_tick(cpu, ts)) {
> tick_nohz_stop_sched_tick(ts, cpu);
> - else if (ts->tick_stopped)
> - tick_nohz_restart_sched_tick(ts, ktime_get());
> + } else {
> + /*
> + * Don't allow the user to think they can get
> + * full NO_HZ with this machine.
> + */
> + WARN_ONCE(tick_nohz_full_running,
> + "NO_HZ_FULL will not work for the current system.");
can_stop_full_tick() returning false can be transient and then the user
still has no idea _why_ this is printed.
Also assume the user/admin starts perf and knows he's going to disturb
NOHZ full, then _why_ would he be interested in that warning.
And again the backtrace is useless. The call path is known.
Thanks,
tglx
next prev parent reply other threads:[~2021-06-22 15:14 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-20 10:13 [PATCH v3] Add kernel logs when sched clock unstable and NO_HZ_FULL is not possible Ani Sinha
2021-06-22 15:14 ` Thomas Gleixner [this message]
2021-06-26 16:18 ` Ani Sinha
2021-07-03 17:30 ` Ani Sinha
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