2017-03-02 09:02:50

by David Engraf

Subject: [PATCH resend] 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 <[email protected]>
---
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

2017-03-23 19:39:07

by John Stultz

Subject: Re: [PATCH resend] timers, sched_clock: Update timeout for clock wrap

On Thu, Mar 2, 2017 at 1:02 AM, David Engraf <[email protected]> wrote:
> 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 <[email protected]>

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

thanks
-john