linux-kernel - [PATCH] sched: Check nr_running before calling pick_next

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Date:	Sat, 02 Jul 2011 00:41:51 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: [PATCH] sched: Check nr_running before calling pick_next_task in
 schedule().

Currently at schedule(), when we call pick_next_task we don't check whether current rq is empty or not. Since idle_balance can fail,
its nice to check whether we really have any task on rq or not. If not, we can call idle_sched_class.pick_next_task straight.

Signed-off-by: Rakib Mullick <rakib.mullick@...il.com>
---

diff --git a/kernel/sched.c b/kernel/sched.c
index 5925275..a4f4f58 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4273,7 +4273,14 @@ need_resched:
 		idle_balance(cpu, rq);
 
 	put_prev_task(rq, prev);
-	next = pick_next_task(rq);
+	/*  Since idle_balance can fail, its better to check rq->nr_running.
+	 *  Otherwise we can call idle_sched_class.pick_next_task straight,
+	 *  cause we need to do some accounting.
+	 */
+	if (likely(rq->nr_running))
+		next = pick_next_task(rq);
+	else
+		next = idle_sched_class.pick_next_task(rq);
 	clear_tsk_need_resched(prev);
 	rq->skip_clock_update = 0;
 


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