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SubjectRe: [RFT][PATCH v4 3/7] sched: idle: Do not stop the tick before cpuidle_idle_call()
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 :)

> 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.

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.

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