Re: [Update 2x] Re: [PATCH v3]PM/Sleep: Timer quiesce in freeze state
From: Peter Zijlstra <peterz@infradead.org>
Date: 2015-02-09 15:44:19
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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.
quoted hunk ↗ jump to hunk
@@ -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.