linux-kernel - [PATCH 1/2 V2] workqueue: remove unneeded test before wake up next worker

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Date:	Tue, 22 Jul 2014 13:01:59 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	<linux-kernel@...r.kernel.org>
CC:	Tejun Heo <tj@...nel.org>, Lai Jiangshan <laijs@...fujitsu.com>
Subject: [PATCH 1/2 V2] workqueue: remove unneeded test before wake up next worker

In this code:
	if ((worker->flags & WORKER_UNBOUND) && need_more_worker(pool))
		wake_up_worker(pool);

the first test is unneeded. Even the first test is removed, it doesn't affect
the wake-up logic when WORKER_UNBOUND. And it will not introduce any useless
wake-up when !WORKER_UNBOUND since the nr_running >= 1 except only one case.
It will introduce useless/redundant wake-up when cpu_intensive, but this
case is rare and next patch will also remove this redundant wake-up.

Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
 kernel/workqueue.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a791a8c..cd75689 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2048,10 +2048,13 @@ __acquires(&pool->lock)
 		worker_set_flags(worker, WORKER_CPU_INTENSIVE, true);
 
 	/*
-	 * Unbound pool isn't concurrency managed and work items should be
-	 * executed ASAP.  Wake up another worker if necessary.
+	 * Wake up another worker if necessary.  It is a no-op
+	 * when the current worker is concurrency managed since
+	 * pool->nr_running >= 1.  But it is required for non-concurrency
+	 * managed workers, mainly for unbound pool which requries
+	 * chain execution of currently pending work items ASAP.
 	 */
-	if ((worker->flags & WORKER_UNBOUND) && need_more_worker(pool))
+	if (need_more_worker(pool))
 		wake_up_worker(pool);
 
 	/*
-- 
1.7.4.4

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