linux-kernel - [PATCH] sched/rt: Decrease number of calls of push_rt_task() in push_rt

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Message-Id: <2016751359330408@web20f.yandex.ru>
Date:	Mon, 28 Jan 2013 03:46:48 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Subject: [PATCH] sched/rt: Decrease number of calls of push_rt_task() in push_rt_tasks()

The patch aims to decrease the number of calls of push_rt_task()
in push_rt_tasks().

It's not necessary to push more than 'num_online_cpus() - 1' tasks.
If just pushed task doesn't leave its new CPU during our local call
of push_rt_tasks() than we won't push another task to the CPU.
If it leave or change priority than it will pull new task by itself.

Signed-off-by: Kirill V Tkhai <tkhai@...dex.ru>
CC: Steven Rostedt <rostedt@...dmis.org>
CC: Ingo Molnar <mingo@...nel.org>
CC: Peter Zijlstra <peterz@...radead.org>
CC: linux-rt-users <linux-rt-users@...r.kernel.org>
---
 kernel/sched/rt.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4e8f0f4..edf046d 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1703,8 +1703,10 @@ out:
 
 static void push_rt_tasks(struct rq *rq)
 {
+	int num_cpus = num_online_cpus() - 1;
+
 	/* push_rt_task will return true if it moved an RT */
-	while (push_rt_task(rq))
+	while (push_rt_task(rq) && --num_cpus > 0)
 		;
 }
 
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