Re: [PATCH 2/3] clockevents: Restart clockevent device before using it again

From: Viresh Kumar
Date: Thu Apr 02 2015 - 09:50:59 EST

On 2 April 2015 at 19:04, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Fri, Mar 27, 2015 at 10:44:28PM +0530, Viresh Kumar wrote:

>> +++ b/kernel/time/hrtimer.c
>> @@ -566,6 +566,7 @@ static int hrtimer_reprogram(struct hrtimer *timer,
>> {

>> + /* Switchback to ONESHOT state */
>> + if (unlikely(dev->state == CLOCK_EVT_STATE_ONESHOT_STOPPED))
>> + clockevents_set_state(dev, CLOCK_EVT_STATE_ONESHOT);
>> +
>> /*
>> * Clockevents returns -ETIME, when the event was in the past.
>> */
> Should we not do this in tick_program_event() instead? Note that there
> are a few more places that call that, the two in the hrtimer_interrupt()
> should be safe because if we're handling the interrupt its cannot be
> stopped anyhow.
> hrtimer_force_reprogram() seems to need the annotation regardless.

Do you mean that we need the same modification here as well? In order
to save myself against any bugs, I have added following to

+ /* We must be in ONESHOT state here */
+ WARN_ONCE(dev->state != CLOCK_EVT_STATE_ONESHOT, "Current state: %d\n",
+ dev->state);

And I never faced this WARN, or any such reports from Fengguang. So
probably after all the hrtimers are gone, we will always call

> Furthermore, by putting it in tick_program_event() you also don't need
> to fixup tick_nohz_restart().
> Or am I completely missing something?

So yes, if we would have done that in tick_program_event(), it would have
been a single place for doing this change..

But, when Thomas ranted [1] at me on this earlier, he said:

No, we are not doing a state change behind the scene and a magic

2B) Implement the ONESHOT_STOPPED logic and make sure all of the core
code is aware of it.

And so I did it explicitly, wherever it is required.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at