linux-kernel - [PATCH 1/5] sched: only try to push a task on wakeup if it is migratable

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Message-ID: <20080825201523.23217.39632.stgit@dev.haskins.net>
Date:	Mon, 25 Aug 2008 16:15:24 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	mingo@...e.hu
Cc:	srostedt@...hat.com, peterz@...radead.org,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	npiggin@...e.de, gregory.haskins@...il.com
Subject: [PATCH 1/5] sched: only try to push a task on wakeup if it is
	migratable

There is no sense in wasting time trying to push a task away that
cannot move anywhere else.  We gain no benefit from trying to push
other tasks at this point, so if the task being woken up is non
migratable, just skip the whole operation.  This reduces overhead
in the wakeup path for certain tasks.

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

 kernel/sched_rt.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 6163e4c..196c024 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1229,14 +1229,16 @@ static void post_schedule_rt(struct rq *rq)
 }
 
 /*
- * If we are not running and we are not going to reschedule soon, we should
- * try to push tasks away now
+ * If we are not running, we are not going to reschedule soon,
+ * and we have tasks that could be pushed, we should try to push tasks
+ * away now
  */
 static void task_wake_up_rt(struct rq *rq, struct task_struct *p)
 {
 	if (!task_running(rq, p) &&
 	    !test_tsk_need_resched(rq->curr) &&
-	    rq->rt.overloaded)
+	    rq->rt.overloaded &&
+	    p->rt.nr_cpus_allowed > 1)
 		push_rt_tasks(rq);
 }
 

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