linux-kernel - [PATCH] timers, sched_clock: Update timeout for clock wrap

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Message-Id: <20170217075103.4707-1-david.engraf@sysgo.com>
Date:   Fri, 17 Feb 2017 08:51:03 +0100
From:   David Engraf <david.engraf@...go.com>
To:     tglx@...utronix.de, john.stultz@...aro.org
Cc:     linux-kernel@...r.kernel.org, David Engraf <david.engraf@...go.com>
Subject: [PATCH] timers, sched_clock: Update timeout for clock wrap

The scheduler clock framework may not use the correct timeout for the clock
wrap. This happens when a new clock driver calls sched_clock_register()
after the kernel called sched_clock_postinit(). In this case the clock wrap
timeout is too long thus sched_clock_poll() is called too late and the clock
already wrapped.

On my ARM system the scheduler was no longer scheduling any other task than
the idle task because the sched_clock() wrapped.

Signed-off-by: David Engraf <david.engraf@...go.com>
---
 kernel/time/sched_clock.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index a26036d..382b159 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -205,6 +205,11 @@ sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)

 	update_clock_read_data(&rd);

+	if (sched_clock_timer.function != NULL) {
+		/* update timeout for clock wrap */
+		hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
+	}
+
 	r = rate;
 	if (r >= 4000000) {
 		r /= 1000000;
-- 
2.9.3