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References: <20210627064911.2179786-1-ani@anisinha.ca>
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From:   Ani Sinha <ani@anisinha.ca>
Date:   Sat, 3 Jul 2021 22:59:56 +0530
Message-ID: <CAARzgwyUb9QgvDKZ+BWG4GnRizn=hyV+0fvsT3ecT8YqvUz3sg@mail.gmail.com>
Subject: Re: [PATCH v1] Print a log when the sched clock is marked unstable
To:     linux-kernel@vger.kernel.org
Cc:     anirban.sinha@nokia.com, Thomas Gleixner <tglx@linutronix.de>,
        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>
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On Sun, Jun 27, 2021 at 12:19 PM Ani Sinha <ani@anisinha.ca> wrote:
>
> 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 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@anisinha.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();
> +       }
>  }
>
>  static void __sched_clock_gtod_offset(void)
> --
> 2.25.1