linux-kernel - [sched/rt] Optimization of function pull_rt

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Date:	Sun, 15 Apr 2012 23:45:22 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	linux-kernel@...r.kernel.org
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: [sched/rt] Optimization of function pull_rt_task()

The condition (src_rq->rt.rt_nr_running) is weak because it doesn't
consider the cases when src_rq has only processes bound to it (when
single cpu is allowed). It may be running kernel thread like
migration/x etc.

So it's better to use more stronger condition which is able to exclude
above conditions. The function has_pushable_tasks() complitely does
this. A task may be pullable for another cpu rq only if he is pushable
for his own queue.

Signed-off-by: Kirill Tkhai <tkhai@...dex.ru>
---
 kernel/sched/rt.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index c5565c3..61e3086 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1729,7 +1729,7 @@ static int pull_rt_task(struct rq *this_rq)
 		/*
 		 * Are there still pullable RT tasks?
 		 */
-		if (src_rq->rt.rt_nr_running <= 1)
+		if (!has_pushable_tasks(src_rq))
 			goto skip;
 
 		p = pick_next_highest_task_rt(src_rq, this_cpu);


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