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From:   Ani Sinha <ani@anisinha.ca>
To:     linux-kernel@vger.kernel.org
Cc:     anirban.sinha@nokia.com, tglx@linutronix.de,
        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>
Subject: [PATCH v2] sched/clock: print a log when the sched clock is marked unstable
Date:   Wed,  7 Jul 2021 16:26:59 +0530
Message-Id: <20210707105659.194171-1-ani@anisinha.ca>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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@anisinha.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);
 }
 
-- 
2.25.1