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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2015-02-13 23:50:43 +0100
committerRafael J. Wysocki <rjw@rjwysocki.net>2015-02-15 19:40:09 +0100
commit124cf9117c5f93cc5b324530b7e105b09c729d5d (patch)
treee3416dc59e678015f41bd9b70dc1a8cc6145ca80 /drivers
parent060407aed56c00960c9b5f70f5d19b2823adffd7 (diff)
PM / sleep: Make it possible to quiesce timers during suspend-to-idle
The efficiency of suspend-to-idle depends on being able to keep CPUs in the deepest available idle states for as much time as possible. Ideally, they should only be brought out of idle by system wakeup interrupts. However, timer interrupts occurring periodically prevent that from happening and it is not practical to chase all of the "misbehaving" timers in a whack-a-mole fashion. A much more effective approach is to suspend the local ticks for all CPUs and the entire timekeeping along the lines of what is done during full suspend, which also helps to keep suspend-to-idle and full suspend reasonably similar. The idea is to suspend the local tick on each CPU executing cpuidle_enter_freeze() and to make the last of them suspend the entire timekeeping. That should prevent timer interrupts from triggering until an IO interrupt wakes up one of the CPUs. It needs to be done with interrupts disabled on all of the CPUs, though, because otherwise the suspended clocksource might be accessed by an interrupt handler which might lead to fatal consequences. Unfortunately, the existing ->enter callbacks provided by cpuidle drivers generally cannot be used for implementing that, because some of them re-enable interrupts temporarily and some idle entry methods cause interrupts to be re-enabled automatically on exit. Also some of these callbacks manipulate local clock event devices of the CPUs which really shouldn't be done after suspending their ticks. To overcome that difficulty, introduce a new cpuidle state callback, ->enter_freeze, that will be guaranteed (1) to keep interrupts disabled all the time (and return with interrupts disabled) and (2) not to touch the CPU timer devices. Modify cpuidle_enter_freeze() to look for the deepest available idle state with ->enter_freeze present and to make the CPU execute that callback with suspended tick (and the last of the online CPUs to execute it with suspended timekeeping). Suggested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/cpuidle/cpuidle.c49
1 files changed, 44 insertions, 5 deletions
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 23a8d6cc8d30..4d534582514e 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -20,6 +20,7 @@
#include <linux/hrtimer.h>
#include <linux/module.h>
#include <linux/suspend.h>
+#include <linux/tick.h>
#include <trace/events/power.h>
#include "cpuidle.h"
@@ -69,18 +70,20 @@ int cpuidle_play_dead(void)
* cpuidle_find_deepest_state - Find deepest state meeting specific conditions.
* @drv: cpuidle driver for the given CPU.
* @dev: cpuidle device for the given CPU.
+ * @freeze: Whether or not the state should be suitable for suspend-to-idle.
*/
static int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
- struct cpuidle_device *dev)
+ struct cpuidle_device *dev, bool freeze)
{
unsigned int latency_req = 0;
- int i, ret = CPUIDLE_DRIVER_STATE_START - 1;
+ int i, ret = freeze ? -1 : CPUIDLE_DRIVER_STATE_START - 1;
for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
struct cpuidle_state *s = &drv->states[i];
struct cpuidle_state_usage *su = &dev->states_usage[i];
- if (s->disabled || su->disable || s->exit_latency <= latency_req)
+ if (s->disabled || su->disable || s->exit_latency <= latency_req
+ || (freeze && !s->enter_freeze))
continue;
latency_req = s->exit_latency;
@@ -89,10 +92,31 @@ static int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
return ret;
}
+static void enter_freeze_proper(struct cpuidle_driver *drv,
+ struct cpuidle_device *dev, int index)
+{
+ tick_freeze();
+ /*
+ * The state used here cannot be a "coupled" one, because the "coupled"
+ * cpuidle mechanism enables interrupts and doing that with timekeeping
+ * suspended is generally unsafe.
+ */
+ drv->states[index].enter_freeze(dev, drv, index);
+ WARN_ON(!irqs_disabled());
+ /*
+ * 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());
+}
+
/**
* cpuidle_enter_freeze - Enter an idle state suitable for suspend-to-idle.
*
- * Find the deepest state available and enter it.
+ * If there are states with the ->enter_freeze callback, find the deepest of
+ * them and enter it with frozen tick. Otherwise, find the deepest state
+ * available and enter it normally.
*/
void cpuidle_enter_freeze(void)
{
@@ -100,7 +124,22 @@ void cpuidle_enter_freeze(void)
struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
int index;
- index = cpuidle_find_deepest_state(drv, dev);
+ /*
+ * Find the deepest state with ->enter_freeze present, which guarantees
+ * that interrupts won't be enabled when it exits and allows the tick to
+ * be frozen safely.
+ */
+ index = cpuidle_find_deepest_state(drv, dev, true);
+ if (index >= 0) {
+ enter_freeze_proper(drv, dev, index);
+ return;
+ }
+
+ /*
+ * It is not safe to freeze the tick, find the deepest state available
+ * at all and try to enter it normally.
+ */
+ index = cpuidle_find_deepest_state(drv, dev, false);
if (index >= 0)
cpuidle_enter(drv, dev, index);
else