linux-kernel - [PATCH 3/3] stop_machine: wake up stopper thread lazily

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Date:	Wed, 6 Feb 2013 20:40:32 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Rusty Russell <rusty@...tcorp.com.au>, Tejun Heo <tj@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Hillf Danton <dhillf@...il.com>
Subject: [PATCH 3/3] stop_machine: wake up stopper thread lazily

Ring no bell if the stopper thread is busy in handling enqueued works.

Signed-off-by: Hillf Danton <dhillf@...il.com>
---

--- a/kernel/stop_machine.c	Wed Feb  6 20:05:44 2013
+++ b/kernel/stop_machine.c	Wed Feb  6 20:06:56 2013
@@ -72,8 +72,10 @@ static void cpu_stop_queue_work(struct c
 	spin_lock_irqsave(&stopper->lock, flags);

 	if (stopper->enabled) {
+		int wakeup = list_empty(&stopper->works);
 		list_add_tail(&work->list, &stopper->works);
-		wake_up_process(stopper->thread);
+		if (wakeup)
+			wake_up_process(stopper->thread);
 	} else
 		cpu_stop_signal_done(work->done, false, 0);

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