linux-kernel - [PATCH] idle: move latency tracing stop/start calls deeper inside the idle loop

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Date:	Fri,  3 Jul 2015 16:19:40 +0200
From:	Lucas Stach <l.stach@...gutronix.de>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel@...gutronix.de, patchwork-lst@...gutronix.de
Subject: [PATCH] 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@...gutronix.de>
---
 drivers/cpuidle/cpuidle.c |  2 ++
 kernel/sched/idle.c       | 14 +++++---------
 2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 61c417b9e53f..d78514ac3f5d 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -173,7 +173,9 @@ 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);
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index fefcb1fa5160..30b799bfc3c6 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -93,12 +93,6 @@ static void cpuidle_idle_call(void)
 	}
 
 	/*
-	 * 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
 	 * step to the grace period
@@ -181,7 +175,6 @@ exit_idle:
 		local_irq_enable();
 
 	rcu_idle_exit();
-	start_critical_timings();
 	return;
 
 use_default:
@@ -189,10 +182,13 @@ use_default:
 	 * We can't use the cpuidle framework, let's use the default
 	 * idle routine.
 	 */
-	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();
+	}
 
 	goto exit_idle;
 }
-- 
2.1.4

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