[PATCH] trace: stop critical timings before idle loop on idle=poll

From	Daniel Bristot de Oliveira <bristot@redhat.com>
Newsgroups	linux.kernel
Subject	[PATCH] trace: stop critical timings before idle loop on idle=poll
Date	2015-10-08 20:40 +0200
Message-ID	<qhogF-3ew-3@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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When using idle=poll, the preemptoff tracer is always showing the idle
task as the culprit for long latencies. That happens because critical
timings are not stopped before idle loop. This patch stops critical
timings before entering the idle loop, starting it again after the
idle loop.

This problem does not affect the irqsoff tracer because interruptions
are enabled before entering the idle loop.

Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Reviewed-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
---
 kernel/sched/idle.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 8f177c7..4a2ef5a 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -57,9 +57,11 @@ static inline int cpu_idle_poll(void)
 	rcu_idle_enter();
 	trace_cpu_idle_rcuidle(0, smp_processor_id());
 	local_irq_enable();
+	stop_critical_timings();
 	while (!tif_need_resched() &&
 		(cpu_idle_force_poll || tick_check_broadcast_expired()))
 		cpu_relax();
+	start_critical_timings();
 	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
 	rcu_idle_exit();
 	return 1;
-- 
2.4.3

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[PATCH] trace: stop critical timings before idle loop on idle=poll Daniel Bristot de Oliveira <bristot@redhat.com> - 2015-10-08 20:40 +0200
  Re: [PATCH] trace: stop critical timings before idle loop on  idle=poll Steven Rostedt <rostedt@goodmis.org> - 2015-10-09 18:40 +0200
  [tip:sched/urgent] sched, tracing: Stop/  start critical timings around the idle=poll idle loop tip-bot for Daniel Bristot de Oliveira <tipbot@zytor.com> - 2015-10-12 10:00 +0200

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