linux-kernel - [PATCH] Prevent immediate process rescheduling

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Message-ID: <200909181449.12311.mark.langsdorf@amd.com>
Date:	Fri, 18 Sep 2009 14:49:12 -0500
From:	Mark Langsdorf <mark.langsdorf@....com>
To:	linux-kernel@...r.kernel.org
Subject: [PATCH] Prevent immediate process rescheduling

Prevent the scheduler from immediately rescheduling a process
that just yielded if there is another process available.

Originally suggested by Mike Galbraith (efault@....de).

Signed-off-by: Mark Langsdorf <mark.langsdorf@....com>
---
 kernel/sched_fair.c |   16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 652e8bd..4fad08f 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -353,11 +353,25 @@ static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 static struct sched_entity *__pick_next_entity(struct cfs_rq *cfs_rq)
 {
 	struct rb_node *left = cfs_rq->rb_leftmost;
+	struct sched_entity *se, *curr;
 
 	if (!left)
 		return NULL;
 
-	return rb_entry(left, struct sched_entity, run_node);
+	se = rb_entry(left, struct sched_entity, run_node);
+	curr = &current->se;
+
+	/* 
+	 * Don't select the entity who just tried to schedule away
+	 * if there's another entity available.
+	 */
+	if (unlikely(se == curr && cfs_rq->nr_running > 1)) {
+		struct rb_node *next_node = rb_next(&curr->run_node);
+		if (next_node)
+			se = rb_entry(next_node, struct sched_entity, run_node);
+	}
+
+	return se;
 }
 
 static struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
-- 
1.6.0.2

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