linux-kernel - [PATCH 3.12 043/116] sched,rt: Remove return value from pull_rt

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Message-Id: <2f61a9e78fc7a18a55cba55a812337c50bb99f24.1457082108.git.jslaby@suse.cz>
Date:	Fri,  4 Mar 2016 10:01:28 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>, ktkhai@...allels.com,
	rostedt@...dmis.org, juri.lelli@...il.com, pang.xunlei@...aro.org,
	oleg@...hat.com, wanpeng.li@...ux.intel.com,
	umgwanakikbuti@...il.com, Thomas Gleixner <tglx@...utronix.de>,
	Byungchul Park <byungchul.park@....com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 043/116] sched,rt: Remove return value from pull_rt_task()

From: Peter Zijlstra <peterz@...radead.org>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 8046d6806247088de5725eaf8a2580b29e50ac5a upstream.

In order to be able to use pull_rt_task() from a callback, we need to
do away with the return value.

Since the return value indicates if we should reschedule, do this
inside the function. Since not all callers currently do this, this can
increase the number of reschedules due rt balancing.

Too many reschedules is not a correctness issues, too few are.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: ktkhai@...allels.com
Cc: rostedt@...dmis.org
Cc: juri.lelli@...il.com
Cc: pang.xunlei@...aro.org
Cc: oleg@...hat.com
Cc: wanpeng.li@...ux.intel.com
Cc: umgwanakikbuti@...il.com
Link: http://lkml.kernel.org/r/20150611124742.679002000@infradead.org
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Byungchul Park <byungchul.park@....com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 kernel/sched/rt.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 25f6d7ae589d..85a09baa8f9f 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1647,14 +1647,15 @@ static void push_rt_tasks(struct rq *rq)
 		;
 }
 
-static int pull_rt_task(struct rq *this_rq)
+static void pull_rt_task(struct rq *this_rq)
 {
-	int this_cpu = this_rq->cpu, ret = 0, cpu;
+	int this_cpu = this_rq->cpu, cpu;
+	bool resched = false;
 	struct task_struct *p;
 	struct rq *src_rq;
 
 	if (likely(!rt_overloaded(this_rq)))
-		return 0;
+		return;
 
 	/*
 	 * Match the barrier from rt_set_overloaded; this guarantees that if we
@@ -1711,7 +1712,7 @@ static int pull_rt_task(struct rq *this_rq)
 			if (p->prio < src_rq->curr->prio)
 				goto skip;
 
-			ret = 1;
+			resched = true;
 
 			deactivate_task(src_rq, p, 0);
 			set_task_cpu(p, this_cpu);
@@ -1727,7 +1728,8 @@ skip:
 		double_unlock_balance(this_rq, src_rq);
 	}
 
-	return ret;
+	if (resched)
+		resched_task(this_rq->curr);
 }
 
 static void pre_schedule_rt(struct rq *rq, struct task_struct *prev)
@@ -1830,8 +1832,7 @@ static void switched_from_rt(struct rq *rq, struct task_struct *p)
 	if (!p->on_rq || rq->rt.rt_nr_running)
 		return;
 
-	if (pull_rt_task(rq))
-		resched_task(rq->curr);
+	pull_rt_task(rq);
 }
 
 void init_sched_rt_class(void)
-- 
2.7.2