linux-kernel - [tip:sched/urgent] sched, tracing: Stop/ start critical timings around the idle=poll idle loop

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Date:	Mon, 12 Oct 2015 00:54:32 -0700
From:	tip-bot for Daniel Bristot de Oliveira <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	bristot@...hat.com, efault@....de, hpa@...or.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	rostedt@...dmis.org, torvalds@...ux-foundation.org,
	peterz@...radead.org, mingo@...nel.org, lgoncalv@...hat.com
Subject: [tip:sched/urgent] sched, tracing: Stop/
 start critical timings around the idle=poll idle loop

Commit-ID:  9babcd7929bc8967ae3bb6093f603b93c2f9958f
Gitweb:     http://git.kernel.org/tip/9babcd7929bc8967ae3bb6093f603b93c2f9958f
Author:     Daniel Bristot de Oliveira <bristot@...hat.com>
AuthorDate: Thu, 8 Oct 2015 15:36:06 -0300
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 12 Oct 2015 09:45:25 +0200

sched, tracing: Stop/start critical timings around the idle=poll idle loop

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@...hat.com>
Reviewed-by: Luis Claudio R. Goncalves <lgoncalv@...hat.com>
Acked-by: Steven Rostedt <rostedt@...dmis.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/10fc3705874aef11dbe152a068b591a7be1899b4.1444314899.git.bristot@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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;
--
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