linux-kernel - [PATCH] RT: Only dirty a cacheline if the priority is actually changing

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Message-ID: <20071017185356.11365.49920.stgit@novell1.haskins.net>
Date:	Wed, 17 Oct 2007 14:54:25 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	RT <linux-rt-users@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Gregory Haskins <ghaskins@...ell.com>
Subject: [PATCH] RT: Only dirty a cacheline if the priority is actually
	changing

Oops...forgot to refresh this patch before mailing it.  Heres the actual
patch.


----


We can avoid dirtying a rq related cacheline with a simple check, so why not.

Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
---

 kernel/sched.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 8c916de..d5dfe21 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -368,7 +368,8 @@ static DEFINE_MUTEX(sched_hotcpu_mutex);
 #if defined(CONFIG_PREEMPT_RT) && defined(CONFIG_SMP)
 static inline void set_rq_prio(struct rq *rq, int prio)
 {
-	rq->highest_prio = prio;
+	if (rq->highest_prio != prio)
+		rq->highest_prio = prio;
 }
 
 static inline void update_rq_prio(struct rq *rq)

-
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