sched: Set skip_clock_update in yield_task_fair()

This is another case where we are on our way to schedule(),
so can save a useless clock update and resulting microscopic
vruntime update.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1321971686.6855.18.camel@marge.simson.net
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 13 insertions, 0 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ca8fd44145ac..db313c33af29 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4547,6 +4547,13 @@ again:
                  */
                 if (preempt && rq != p_rq)
                         resched_task(p_rq->curr);
+        } else {
+                /*
+                 * We might have set it in task_yield_fair(), but are
+                 * not going to schedule(), so don't want to skip
+                 * the next update.
+                 */
+                rq->skip_clock_update = 0;
         }
 
 out:
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8e534a05e3ed..81ccb811afb4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3075,6 +3075,12 @@ static void yield_task_fair(struct rq *rq)
                  * Update run-time statistics of the 'current'.
                  */
                 update_curr(cfs_rq);
+                /*
+                 * Tell update_rq_clock() that we've just updated,
+                 * so we don't do microscopic update in schedule()
+                 * and double the fastpath cost.
+                 */
+                 rq->skip_clock_update = 1;
         }
 
         set_skip_buddy(se);