Re: [PATCH 0/2] drivers: cpuidle: minor suspend-to-idle fixes

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Friday, February 27, 2015 10:00:00 AM Lorenzo Pieralisi wrote:
> [CC'ed Preeti]
> 
> On Thu, Feb 26, 2015 at 11:37:54PM +0000, Rafael J. Wysocki wrote:
> > Me versions of the two $subject patches follow.
> 
> Thank you. I am testing them and I have run into the following issue.
> 
> Starting with:
> 
> 3810631 ("PM / sleep: Re-implement suspend-to-idle handling")
> 
> the suspend-to-idle code path in the cpuidle_idle_call() bypasses
> the CPUIDLE_FLAG_TIMER_STOP code path entirely.

Hmm, this looks like a mistake.  Sorry about that.

> Now, on most of
> the current ARM platforms, the deepest idle state loses the tick device
> context, therefore this means that going to idle through
> suspend-to-idle becomes a brute force way of nuking the tick,
> unless I am missing something here.
> 
> I am experiencing hangs on resume from suspend-to-idle when the broadcast
> timer is the broadast-hrtimer (ie there is no HW broadcast timer in the
> platform) and the deepest idle states lose the tick device context (ie
> they are CPUIDLE_FLAG_TIMER_STOP), I hope Preeti can help me test this on
> Power, still chasing the issue.
> 
> I could not reproduce the issue with a HW broadcast timer device.
> 
> Platform has deepest idle states that allow CPUs shutdown where the
> local tick device is gone on entry, I am trying to provide you with a
> backtrace, I need time to debug.
> 
> The question I have: is it safe to bypass the CPUIDLE_FLAG_TIMER_STOP
> and related broadcast mode entry/exit in the suspend-to-idle path ?
> 
> I do not think it is, but I am asking.

It isn't in general, but it would be OK in the enter_freeze_proper() path
where the tick is suspended anyway.

> I can "force" tick freeze by initializing the enter_freeze pointer
> in the idle states (that's the next thing I will test), but still, for
> platforms where that's not possible my question above is still valid.

Right.

Does the patch below help (on top of the previous ones)?

Rafael


---
 drivers/cpuidle/cpuidle.c |   31 ++++++++++++++++++++++++++-----
 kernel/sched/idle.c       |   17 ++---------------
 2 files changed, 28 insertions(+), 20 deletions(-)

Index: linux-pm/drivers/cpuidle/cpuidle.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/cpuidle.c
+++ linux-pm/drivers/cpuidle/cpuidle.c
@@ -230,15 +230,36 @@ int cpuidle_select(struct cpuidle_driver
  * @dev:   the cpuidle device
  * @index: the index in the idle state table
  *
- * Returns the index in the idle state, < 0 in case of error.
- * The error code depends on the backend driver
+ * Returns the index in the idle state, < 0 in case of error.  -EBUSY is
+ * returned to indicate that the target state was temporarily unavailable.
+ * The other error codes depend on the backend driver.
  */
 int cpuidle_enter(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 		  int index)
 {
-	if (cpuidle_state_is_coupled(dev, drv, index))
-		return cpuidle_enter_state_coupled(dev, drv, index);
-	return cpuidle_enter_state(dev, drv, index);
+	unsigned int broadcast;
+	int ret;
+
+	broadcast = drv->states[index].flags & CPUIDLE_FLAG_TIMER_STOP;
+
+	/*
+	 * Tell the time framework to switch to a broadcast timer
+	 * because our local timer will be shutdown. If a local timer
+	 * is used from another cpu as a broadcast timer, this call may
+	 * fail if it is not available
+	 */
+	if (broadcast &&
+	    clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu))
+		return -EBUSY;
+
+	ret = cpuidle_state_is_coupled(dev, drv, index) ?
+		cpuidle_enter_state_coupled(dev, drv, index) :
+		cpuidle_enter_state(dev, drv, index);
+
+	if (broadcast)
+		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
+
+	return ret;
 }
 
 /**
Index: linux-pm/kernel/sched/idle.c
===================================================================
--- linux-pm.orig/kernel/sched/idle.c
+++ linux-pm/kernel/sched/idle.c
@@ -81,7 +81,6 @@ static void cpuidle_idle_call(void)
 	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
 	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
 	int next_state, entered_state;
-	unsigned int broadcast;
 
 	/*
 	 * Check if the idle task must be rescheduled. If it is the
@@ -151,18 +150,6 @@ use_default:
 		goto exit_idle;
 	}
 
-	broadcast = drv->states[next_state].flags & CPUIDLE_FLAG_TIMER_STOP;
-
-	/*
-	 * Tell the time framework to switch to a broadcast timer
-	 * because our local timer will be shutdown. If a local timer
-	 * is used from another cpu as a broadcast timer, this call may
-	 * fail if it is not available
-	 */
-	if (broadcast &&
-	    clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu))
-		goto use_default;
-
 	/* Take note of the planned idle state. */
 	idle_set_state(this_rq(), &drv->states[next_state]);
 
@@ -176,8 +163,8 @@ use_default:
 	/* The cpu is no longer idle or about to enter idle. */
 	idle_set_state(this_rq(), NULL);
 
-	if (broadcast)
-		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
+	if (entered_state == -EBUSY)
+		goto use_default;
 
 	/*
 	 * Give the governor an opportunity to reflect on the outcome