[ 033/180] sched: Fix signed unsigned comparison in check_preempt_tick()

[Willy Tarreau]

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Mike Galbraith <efault@xxxxxx>

commit d7d8294415f0ce4254827d4a2a5ee88b00be52a8 upstream.

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@xxxxxxxxxx>
Signed-off-by: Mike Galbraith <efault@xxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
LKML-Reference: <1294202477.9384.5.camel@xxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Willy Tarreau <w@xxxxxx>
---
 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 cd9a40b..fd6e5f2 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -862,6 +862,9 @@ 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);
 	}
-- 
1.7.2.1.45.g54fbc



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