linux-kernel - [PATCH 3/3] cpuidle: Select a different state on tick_broadcast

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Date:	Sun, 10 May 2015 01:19:52 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>, peterz@...radead.org
Cc:	tglx@...utronix.de, rafael.j.wysocki@...el.com,
	daniel.lezcano@...aro.org, rlippert@...gle.com,
	linux-pm@...r.kernel.org, linus.walleij@...aro.org,
	linux-kernel@...r.kernel.org, mingo@...hat.com,
	sudeep.holla@....com, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 3/3] cpuidle: Select a different state on tick_broadcast_enter() failures

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

If tick_broadcast_enter() fails in cpuidle_enter_state(),
try to find another idle state to enter instead of invoking
default_idle_call() immediately and returning -EBUSY which
should increase the chances of saving some energy in those
cases.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/cpuidle/cpuidle.c |   20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

Index: linux-pm/drivers/cpuidle/cpuidle.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/cpuidle.c
+++ linux-pm/drivers/cpuidle/cpuidle.c
@@ -73,7 +73,10 @@ int cpuidle_play_dead(void)
 }
 
 static int find_deepest_state(struct cpuidle_driver *drv,
-			      struct cpuidle_device *dev, bool freeze)
+			      struct cpuidle_device *dev,
+			      unsigned int max_latency,
+			      unsigned int forbidden_flags,
+			      bool freeze)
 {
 	unsigned int latency_req = 0;
 	int i, ret = freeze ? -1 : CPUIDLE_DRIVER_STATE_START - 1;
@@ -83,6 +86,8 @@ static int find_deepest_state(struct cpu
 		struct cpuidle_state_usage *su = &dev->states_usage[i];
 
 		if (s->disabled || su->disable || s->exit_latency <= latency_req
+		    || s->exit_latency > max_latency
+		    || (s->flags & forbidden_flags)
 		    || (freeze && !s->enter_freeze))
 			continue;
 
@@ -100,7 +105,7 @@ static int find_deepest_state(struct cpu
 int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
 			       struct cpuidle_device *dev)
 {
-	return find_deepest_state(drv, dev, false);
+	return find_deepest_state(drv, dev, UINT_MAX, 0, false);
 }
 
 static void enter_freeze_proper(struct cpuidle_driver *drv,
@@ -139,7 +144,7 @@ int cpuidle_enter_freeze(struct cpuidle_
 	 * that interrupts won't be enabled when it exits and allows the tick to
 	 * be frozen safely.
 	 */
-	index = find_deepest_state(drv, dev, true);
+	index = find_deepest_state(drv, dev, UINT_MAX, 0, true);
 	if (index >= 0)
 		enter_freeze_proper(drv, dev, index);
 
@@ -168,8 +173,13 @@ int cpuidle_enter_state(struct cpuidle_d
 	 * CPU as a broadcast timer, this call may fail if it is not available.
 	 */
 	if (broadcast && tick_broadcast_enter()) {
-		default_idle_call();
-		return -EBUSY;
+		index = find_deepest_state(drv, dev, target_state->exit_latency,
+					   CPUIDLE_FLAG_TIMER_STOP, false);
+		if (index < 0) {
+			default_idle_call();
+			return -EBUSY;
+		}
+		target_state = &drv->states[index];
 	}
 
 	/* Take note of the planned idle state. */
--
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