linux-kernel - [PATCH 1/7] Avoid taking rq lock in wake_priority

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Date:	Fri, 27 Oct 2006 19:41:17 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	akpm@...l.org
Cc:	Peter Williams <pwil3058@...pond.net.au>,
	linux-kernel@...r.kernel.org,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Christoph Lameter <clameter@....com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Ingo Molnar <mingo@...e.hu>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
Subject: [PATCH 1/7] Avoid taking rq lock in wake_priority_sleeper

Avoid taking the rq lock in wake_priority sleeper

Avoid taking the request queue lock in wake_priority_sleeper if
there are no running processes.

Signed-off-by: Christoph Lameter <clameter@....com>

Index: linux-2.6.19-rc3/kernel/sched.c
===================================================================
--- linux-2.6.19-rc3.orig/kernel/sched.c	2006-10-26 21:30:11.328325096 -0500
+++ linux-2.6.19-rc3/kernel/sched.c	2006-10-27 11:58:02.142767971 -0500
@@ -2898,6 +2898,9 @@ static inline int wake_priority_sleeper(
 	int ret = 0;
 
 #ifdef CONFIG_SCHED_SMT
+	if (!rq->nr_running)
+		return 0;
+
 	spin_lock(&rq->lock);
 	/*
 	 * If an SMT sibling task has been put to sleep for priority
-
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