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SubjectRe: [Update 2x] Re: [PATCH v3]PM/Sleep: Timer quiesce in freeze state
On Mon, Feb 09, 2015 at 03:54:22AM +0100, Rafael J. Wysocki wrote:
> Complete patch with that modification is appended. In the next few days I'm
> going to split it into smaller parts and send along with cpuidle driver
> patches implementing ->enter_freeze.
>
> Please let me know what you think.

> @@ -104,6 +105,21 @@ static void cpuidle_idle_call(void)
> rcu_idle_enter();
>
> /*
> + * Suspend-to-idle ("freeze") is a system state in which all user space
> + * has been frozen, all I/O devices have been suspended and the only
> + * activity happens here and in iterrupts (if any). In that case bypass
> + * the cpuidle governor and go stratight for the deepest idle state
> + * available. Possibly also suspend the local tick and the entire
> + * timekeeping to prevent timer interrupts from kicking us out of idle
> + * until a proper wakeup interrupt happens.
> + */
> + if (idle_should_freeze()) {
> + cpuidle_enter_freeze();
> + local_irq_enable();
> + goto exit_idle;
> + }
> +
> + /*
> * Ask the cpuidle framework to choose a convenient idle state.
> * Fall back to the default arch idle method on errors.
> */

I was hoping to not have to put that into the regular idle path; say
maybe share a single special branch with the play-dead call. People seem
to start complaining about the total amount of time it takes to just
'run' the idle path.

Now I don't think we can do that, because we need the
arch_cpu_idle_enter() nonsense for the one but not the other; also all
this really only makes sense in the cpuidle context, so nothing to be
done about that.

In any case, you could make that:

static inline bool idle_should_freeze(void)
{
return unlikely(suspend_freeze_state == FREEZE_STATE_ENTER);
}

which should help a bit I suppose.

> +static void enter_freeze_proper(struct cpuidle_driver *drv,
> + struct cpuidle_device *dev, int index)
> +{
> + tick_freeze();
> + drv->states[index].enter_freeze(dev, drv, index);

This is slightly different from cpuidle_enter() in that it does not
consider the coupled states nonsense, is that on purpose? And if so,
does that want a comment?

> + /*
> + * timekeeping_resume() that will be called by tick_unfreeze() for the
> + * last CPU executing it calls functions containing RCU read-side
> + * critical sections, so tell RCU about that.
> + */
> + RCU_NONIDLE(tick_unfreeze());
> +}


But over all it looks fine to me.


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