[tip:sched/core] sched: Add a lock break for PREEMPT=y

[tip-bot for Peter Zijlstra]

Commit-ID:  baa8c1102f0cd86e69c1497d61d2ee177e663663
Gitweb:     http://git.kernel.org/tip/baa8c1102f0cd86e69c1497d61d2ee177e663663
Author:     Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Thu, 17 Dec 2009 18:10:09 +0100
Committer:  Ingo Molnar <mingo@xxxxxxx>
CommitDate: Thu, 21 Jan 2010 13:40:13 +0100

sched: Add a lock break for PREEMPT=y

Since load-balancing can hold rq->locks for quite a long while, allow
breaking out early when there is lock contention.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 kernel/sched_fair.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 93fccba..65d0820 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2065,6 +2065,10 @@ static int move_tasks(struct rq *this_rq, int this_cpu, struct rq *busiest,
 		 */
 		if (idle == CPU_NEWLY_IDLE && this_rq->nr_running)
 			break;
+
+		if (raw_spin_is_contended(&this_rq->lock) ||
+				raw_spin_is_contended(&busiest->lock))
+			break;
 #endif
 	} while (load_moved && max_load_move > total_load_moved);
 
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