idle / sleep: Avoid excessive disabling and enabling interrupts

Disabling interrupts at the end of cpuidle_enter_freeze() is not
useful, because its caller, cpuidle_idle_call(), re-enables them
right away after invoking it.

To avoid that unnecessary back and forth dance with interrupts,
make cpuidle_enter_freeze() enable interrupts after calling
enter_freeze_proper() and drop the local_irq_disable() at its
end, so that all of the code paths in it end up with interrupts
enabled.  Then, cpuidle_idle_call() will not need to re-enable
interrupts after calling cpuidle_enter_freeze() any more, because
the latter will return with interrupts enabled, in analogy with
cpuidle_enter().

Reported-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 4d53458..b573f58 100644 (file)
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -117,6 +117,8 @@ static void enter_freeze_proper(struct cpuidle_driver *drv,
  * 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.
+ *
+ * Returns with enabled interrupts.
  */
 void cpuidle_enter_freeze(void)
 {
@@ -132,6 +134,7 @@ void cpuidle_enter_freeze(void)
        index = cpuidle_find_deepest_state(drv, dev, true);
        if (index >= 0) {
                enter_freeze_proper(drv, dev, index);
+               local_irq_enable();
                return;
        }
 
@@ -144,9 +147,6 @@ void cpuidle_enter_freeze(void)
                cpuidle_enter(drv, dev, index);
        else
                arch_cpu_idle();
-
-       /* Interrupts are enabled again here. */
-       local_irq_disable();
 }
 
 /**

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 94b2d7b..f59198b 100644 (file)
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -116,7 +116,6 @@ static void cpuidle_idle_call(void)
         */
        if (idle_should_freeze()) {
                cpuidle_enter_freeze();
-               local_irq_enable();
                goto exit_idle;
        }