linux-kernel - [PATCH] small optimization to update_curr

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Date:	Fri, 31 Oct 2008 08:03:41 -0500
From:	Dimitri Sivanich <sivanich@....com>
To:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] small optimization to update_curr_rt

A very minor improvement, but might it be better to check sched_rt_runtime(rt_rq)
before taking the rt_runtime_lock?

Signed-off-by: Dimitri Sivanich <sivanich@....com>

--

 kernel/sched_rt.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux/kernel/sched_rt.c
===================================================================
--- linux.orig/kernel/sched_rt.c	2008-10-22 16:10:03.000000000 -0500
+++ linux/kernel/sched_rt.c	2008-10-31 07:57:19.000000000 -0500
@@ -537,13 +537,13 @@ static void update_curr_rt(struct rq *rq
 	for_each_sched_rt_entity(rt_se) {
 		rt_rq = rt_rq_of_se(rt_se);
 
-		spin_lock(&rt_rq->rt_runtime_lock);
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
+			spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
 			if (sched_rt_runtime_exceeded(rt_rq))
 				resched_task(curr);
+			spin_unlock(&rt_rq->rt_runtime_lock);
 		}
-		spin_unlock(&rt_rq->rt_runtime_lock);
 	}
 }
 
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