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.

---
 kernel/time/sched_clock.c | 5 +++++
 1 file changed, 5 insertions(+)

index a26036d..382b159 100644
@@ -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

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.

---
 kernel/time/sched_clock.c | 5 +++++
 1 file changed, 5 insertions(+)

index a26036d..382b159 100644
@@ -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

Thanks for sending this in! It looks sane, so I've queued it.

thanks
-john