[tip:sched/urgent] sched: Fix signed unsigned comparison in check_preempt_tick()

[tip-bot for Mike Galbraith <efault@gmx.de>]

Commit-ID:  d7d8294415f0ce4254827d4a2a5ee88b00be52a8
Gitweb:     http://git.kernel.org/tip/d7d8294415f0ce4254827d4a2a5ee88b00be52a8
Author:     Mike Galbraith <efault@gmx.de>
AuthorDate: Wed, 5 Jan 2011 05:41:17 +0100
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Tue, 18 Jan 2011 15:09:44 +0100

sched: Fix signed unsigned comparison in check_preempt_tick()

Signed unsigned comparison may lead to superfluous resched if leftmost
is right of the current task, wasting a few cycles, and inadvertently
_lengthening_ the current task's slice.

Reported-by: Venkatesh Pallipadi <venki@google.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1294202477.9384.5.camel@marge.simson.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/sched_fair.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 414145c..77e9166 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1062,6 +1062,9 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
 		struct sched_entity *se = __pick_next_entity(cfs_rq);
 		s64 delta = curr->vruntime - se->vruntime;
 
+		if (delta < 0)
+			return;
+
 		if (delta > ideal_runtime)
 			resched_task(rq_of(cfs_rq)->curr);
 	}