sched/idle: Move latency tracing stop/start calls deeper inside the idle loop

Make sure to stop tracing only once we are past a point where
all latency tracing events have been processed (irqs are not
enabled again). This has the slight advantage of capturing more
latency related events in the idle path, but most importantly it
makes sure that latency tracing doesn't get re-enabled
inadvertently when new events are coming in.

This makes the irqsoff latency tracer useful again, as we stop
capturing CPU sleep time as IRQ latency.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel@pengutronix.de
Cc: patchwork-lst@pengutronix.de
Link: http://lkml.kernel.org/r/1437410090-3747-1-git-send-email-l.stach@pengutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

drivers/cpuidle/cpuidle.c

@@ -118,6 +118,7 @@ static void enter_freeze_proper(struct cpuidle_driver *drv,
 	 * cpuidle mechanism enables interrupts and doing that with timekeeping
 	 * suspended is generally unsafe.
 	 */
+	stop_critical_timings();
 	drv->states[index].enter_freeze(dev, drv, index);
 	WARN_ON(!irqs_disabled());
 	/*
@@ -126,6 +127,7 @@ static void enter_freeze_proper(struct cpuidle_driver *drv,
 	 * critical sections, so tell RCU about that.
 	 */
 	RCU_NONIDLE(tick_unfreeze());
+	start_critical_timings();
 }
 
 /**
@@ -190,7 +192,9 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
 	trace_cpu_idle_rcuidle(index, dev->cpu);
 	time_start = ktime_get();
 
+	stop_critical_timings();
 	entered_state = target_state->enter(dev, drv, index);
+	start_critical_timings();
 
 	time_end = ktime_get();
 	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);

kernel/sched/idle.c

@@ -83,10 +83,13 @@ void __weak arch_cpu_idle(void)
  */
 void default_idle_call(void)
 {
-	if (current_clr_polling_and_test())
+	if (current_clr_polling_and_test()) {
 		local_irq_enable();
-	else
+	} else {
+		stop_critical_timings();
 		arch_cpu_idle();
+		start_critical_timings();
+	}
 }
 
 static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
@@ -140,12 +143,6 @@ static void cpuidle_idle_call(void)
 		return;
 	}
 
-	/*
-	 * During the idle period, stop measuring the disabled irqs
-	 * critical sections latencies
-	 */
-	stop_critical_timings();
-
 	/*
 	 * Tell the RCU framework we are entering an idle section,
 	 * so no more rcu read side critical sections and one more
@@ -198,7 +195,6 @@ exit_idle:
 		local_irq_enable();
 
 	rcu_idle_exit();
-	start_critical_timings();
 }
 
 DEFINE_PER_CPU(bool, cpu_dead_idle);