linux-kernel - Re: [PATCH v2] sched/clock: print a log when the sched clock is marked unstable

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Date:   Wed, 7 Jul 2021 13:17:46 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ani Sinha <ani@...sinha.ca>
Cc:     linux-kernel@...r.kernel.org, anirban.sinha@...ia.com,
        tglx@...utronix.de, Ingo Molnar <mingo@...hat.com>,
        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>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH v2] sched/clock: print a log when the sched clock is
 marked unstable

On Wed, Jul 07, 2021 at 04:26:59PM +0530, Ani Sinha wrote:
> When the sched clock transitions from stable to unstable and
> vice versa, a kernel log is printed. When the sched clock
> is marked explicitly as unstable, make __clear_sched_clock_stable()
> emit a warning log. It is useful for example in understanding
> why a certain feature like NOHZ that depends on availability of a
> stable sched clock, is not available.
> 
> Signed-off-by: Ani Sinha <ani@...sinha.ca>
> ---
>  kernel/sched/clock.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> Changelog:
> V1: original patch
> v2: print pr_warn from __clear_sched_clock_stable instead. Commit log
>     updated with proper prefix and wording.
> 
> diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
> index c2b2859ddd82..99484fec0335 100644
> --- a/kernel/sched/clock.c
> +++ b/kernel/sched/clock.c
> @@ -183,6 +183,7 @@ static void __clear_sched_clock_stable(void)
>  		return;
>  
>  	tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE);
> +	pr_warn("sched_clock: Marking unstable.\n");
>  	schedule_work(&sched_clock_work);
>  }

I'm confused... that work has a ton of printk()s in, what is this
pr_warn() adding?