linux-kernel - [tip:sched/core] sched/idle: Add missing checks to the exit condition of cpu_idle

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Date:	Sun, 1 Feb 2015 09:53:02 -0800
From:	tip-bot for Preeti U Murthy <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	tglx@...utronix.de, preeti@...ux.vnet.ibm.com,
	peterz@...radead.org, mingo@...nel.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	hpa@...or.com
Subject: [tip:sched/core] sched/idle:
  Add missing checks to the exit condition of cpu_idle_poll()

Commit-ID:  ff6f2d29bd31cdfa1ac494a8b26d2af8ba887d59
Gitweb:     http://git.kernel.org/tip/ff6f2d29bd31cdfa1ac494a8b26d2af8ba887d59
Author:     Preeti U Murthy <preeti@...ux.vnet.ibm.com>
AuthorDate: Wed, 21 Jan 2015 16:27:25 +0530
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 30 Jan 2015 19:38:52 +0100

sched/idle: Add missing checks to the exit condition of cpu_idle_poll()

cpu_idle_poll() is entered into when either the cpu_idle_force_poll is set or
tick_check_broadcast_expired() returns true. The exit condition from
cpu_idle_poll() is tif_need_resched().

However this does not take into account scenarios where cpu_idle_force_poll
changes or tick_check_broadcast_expired() returns false, without setting
the resched flag. So a cpu will be caught in cpu_idle_poll() needlessly,
thereby wasting power. Add an explicit check on cpu_idle_force_poll and
tick_check_broadcast_expired() to the exit condition of cpu_idle_poll()
to avoid this.

Signed-off-by: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/20150121105655.15279.59626.stgit@preeti.in.ibm.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/idle.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index c47fce7..aaf1c1d 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -47,7 +47,8 @@ static inline int cpu_idle_poll(void)
 	rcu_idle_enter();
 	trace_cpu_idle_rcuidle(0, smp_processor_id());
 	local_irq_enable();
-	while (!tif_need_resched())
+	while (!tif_need_resched() &&
+		(cpu_idle_force_poll || tick_check_broadcast_expired()))
 		cpu_relax();
 	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
 	rcu_idle_exit();
--
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