linux-kernel - [PATCH V2 3/3] workqueue: Schedule work on non-idle cpu instead of current one

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Date:	Thu, 27 Sep 2012 14:34:05 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	linux-kernel@...r.kernel.org
Cc:	pjt@...gle.com, paul.mckenney@...aro.org, tglx@...utronix.de,
	tj@...nel.org, suresh.b.siddha@...el.com, venki@...gle.com,
	mingo@...hat.com, peterz@...radead.org, robin.randhawa@....com,
	Steve.Bannister@....com, Arvind.Chauhan@....com,
	amit.kucheria@...aro.org, vincent.guittot@...aro.org,
	linaro-dev@...ts.linaro.org, patches@...aro.org,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: [PATCH V2 3/3] workqueue: Schedule work on non-idle cpu instead of current one

Workqueues queues work on current cpu, if the caller haven't passed a preferred
cpu. This may wake up an idle CPU, which is actually not required.

This work can be processed by any CPU and so we must select a non-idle CPU here.
This patch adds in support in workqueue framework to get preferred CPU details
from the scheduler, instead of using current CPU.

Most of the time when a work is queued, the current cpu isn't idle and so we
will choose it only. There are cases when a cpu is idle when it queues some
work. For example, consider following scenario:
- A cpu has programmed a timer and is IDLE now.
- CPU gets into interrupt handler due to timer and queues a work. As the CPU is
  currently IDLE, we can queue this work to some other CPU.

Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 kernel/workqueue.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 143fd8c..5fa4ba4 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1238,7 +1238,7 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
 		struct global_cwq *last_gcwq;
 
 		if (cpu == WORK_CPU_UNBOUND)
-			cpu = raw_smp_processor_id();
+			cpu = sched_select_cpu(0);
 
 		/*
 		 * It's multi cpu.  If @work was previously on a different
-- 
1.7.12.rc2.18.g61b472e


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