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Subject[patch 3/7] sched: set skip_clock_update in yield_task_fair()
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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>

---
kernel/sched/core.c | 8 +++++++-
kernel/sched/fair.c | 6 ++++++
2 files changed, 13 insertions(+), 1 deletion(-)
Index: linux-3.0-tip/kernel/sched/core.c
===================================================================
--- linux-3.0-tip.orig/kernel/sched/core.c
+++ linux-3.0-tip/kernel/sched/core.c
@@ -4547,7 +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:
double_rq_unlock(rq, p_rq);
Index: linux-3.0-tip/kernel/sched/fair.c
===================================================================
--- linux-3.0-tip.orig/kernel/sched/fair.c
+++ linux-3.0-tip/kernel/sched/fair.c
@@ -3062,6 +3062,12 @@ static void yield_task_fair(struct rq *r
* 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);



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