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

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Date:   Wed,  7 Jul 2021 16:26:59 +0530
From:   Ani Sinha <ani@...sinha.ca>
To:     linux-kernel@...r.kernel.org
Cc:     anirban.sinha@...ia.com, tglx@...utronix.de,
        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: [PATCH v2] sched/clock: print a log when the sched clock is marked unstable

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);
 }
 
-- 
2.25.1