linux-kernel - Re: [PATCH v1] Print a log when the sched clock is marked unstable

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Date:   Wed, 07 Jul 2021 12:12:46 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ani Sinha <ani@...sinha.ca>, linux-kernel@...r.kernel.org
Cc:     anirban.sinha@...ia.com, Ani Sinha <ani@...sinha.ca>,
        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>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH v1] Print a log when the sched clock is marked unstable

Ani,

On Sun, Jun 27 2021 at 12:19, Ani Sinha wrote:

I asked you to read Documentation/process carefully and I told you:

        Also your subject line want's a proper prefix.

Your patch is missing a prefix again. Hint:

  git log kernel/sched/clock.c

> In other parts of the kernel when the sched clock transitions from
> stable to unstable and vice versa, a kernel info log is printed.  When
> the sched clock is marked explicitly as unstable, we should print an
> information log as well. This patch addresses this. It is useful in

git grep 'This patch' Documentation/process/

Also please avoid the 'we' wording. 'We should print' does not make
sense if you really think about it.

> cases where for example, we want to understand why a certain feature
> like NOHZ, which depends on a stable sched clock, is not available.
>
> Signed-off-by: Ani Sinha <ani@...sinha.ca>
> ---
>  kernel/sched/clock.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> See also thread
> https://lkml.org/lkml/2021/6/20/32
>
> diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
> index c2b2859ddd82..5a403b2c9b3f 100644
> --- a/kernel/sched/clock.c
> +++ b/kernel/sched/clock.c
> @@ -192,8 +192,10 @@ 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) {
> +		pr_info("sched_clock: Marking unstable.\n");
>  		__clear_sched_clock_stable();

Why isn't that in __clear_sched_clock_stable() ?

Thanks,

        tglx