linux-kernel - [PATCH] sched: fair scheduler should not resched rt tasks

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Message-ID: <alpine.DEB.1.10.0810110258310.12625@gandalf.stny.rr.com>
Date:	Sat, 11 Oct 2008 03:01:50 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Clark Williams <clark.williams@...il.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH] sched: fair scheduler should not resched rt tasks


Using ftrace, I noticed latencies in real-time tasks where they were
needlessly calling schedule due to sched_fair sending out time slices.

This patch prevents a call to resched_task by the sched fair class if
the task it wants to reschedule is an rt task.

Signed-off-by: Steven Rostedt <srostedt@...hat.com>
---
 kernel/sched_fair.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-compile.git/kernel/sched_fair.c
===================================================================
--- linux-compile.git.orig/kernel/sched_fair.c	2008-10-11 02:54:01.000000000 -0400
+++ linux-compile.git/kernel/sched_fair.c	2008-10-11 02:55:52.000000000 -0400
@@ -889,7 +889,7 @@ static void hrtick_start_fair(struct rq 
 		s64 delta = slice - ran;
 
 		if (delta < 0) {
-			if (rq->curr == p)
+			if (rq->curr == p && !rt_task(p))
 				resched_task(p);
 			return;
 		}
--
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