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SubjectRe: [RFT][PATCH v4 3/7] sched: idle: Do not stop the tick before cpuidle_idle_call()
On Thu, Mar 15, 2018 at 7:19 PM, Frederic Weisbecker
<frederic@kernel.org> wrote:
> On Mon, Mar 12, 2018 at 10:53:25AM +0100, Rafael J. Wysocki wrote:
>> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>
>> Make cpuidle_idle_call() decide whether or not to stop the tick.
>>
>> First, the cpuidle_enter_s2idle() path deals with the tick (and with
>> the entire timekeeping for that matter) by itself and it doesn't need
>> the tick to be stopped beforehand.
>
> Not sure you meant timekeeping either :)

Yeah, I meant nohz.

>> if (idle_should_enter_s2idle() || dev->use_deepest_state) {
>> if (idle_should_enter_s2idle()) {
>> + rcu_idle_enter();
>> +
>> entered_state = cpuidle_enter_s2idle(drv, dev);
>> if (entered_state > 0) {
>> local_irq_enable();
>> goto exit_idle;
>> }
>> +
>> + rcu_idle_exit();
>> }
>
> I'm not sure how the tick is stopped on suspend to idle. Perhaps through
> hrtimer (tick_cancel_sched_timer()) or clockevents code.

The latter.

It does clockevents_shutdown() down the road, eventually.

IOW, it couldn't care less. :-)

> But we may have a similar problem than with idle_poll() called right after
> call_cpuidle(). Ie: we arrive in cpuidle_enter_s2idle() with a tick that
> should be reprogrammed while it is not. No idea if that can hurt somehow.
>
> I guess it depends what happens to the tick on s2idle, I'm not clear with that.

No problem there, AFAICS.

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