[RFC/PATCH 17/17] sched: fair: optimize the elegebility test

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

[-- Attachment #1: sched-fair-avg_runtime-opt.patch --]
[-- Type: text/plain, Size: 1361 bytes --]

Suggested by Dmitry Adamushko; trade a div for a mult.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 kernel/sched_fair.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

Index: linux-2.6-2/kernel/sched_fair.c
===================================================================
--- linux-2.6-2.orig/kernel/sched_fair.c
+++ linux-2.6-2/kernel/sched_fair.c
@@ -339,6 +339,12 @@ s64 avg_vruntime(struct cfs_root_rq *cfs
 }
 
 static inline
+int avg_vruntime_cmp(struct cfs_root_rq *cfs_r_rq, s64 vruntime)
+{
+	return (vruntime * cfs_r_rq->nr_queued) <= cfs_r_rq->avg_vruntime;
+}
+
+static inline
 s64 entity_deadline_key(struct cfs_root_rq *cfs_r_rq, struct sched_entity *se)
 {
 	return se->vruntime + se->vperiod - cfs_r_rq->min_vruntime;
@@ -430,11 +436,10 @@ static struct sched_entity *__pick_next_
  */
 static struct sched_entity *__pick_next_entity(struct cfs_root_rq *cfs_r_rq)
 {
-	struct sched_entity *next_deadline;
-	s64 avg = avg_vruntime(cfs_r_rq);
+	struct sched_entity *next_deadline = __pick_next_deadline(cfs_r_rq);
+	s64 vruntime = entity_timeline_key(cfs_r_rq, next_deadline);
 
-	next_deadline = __pick_next_deadline(cfs_r_rq);
-	if (entity_timeline_key(cfs_r_rq, next_deadline) <= avg)
+	if (avg_vruntime_cmp(cfs_r_rq, vruntime))
 		return next_deadline;
 
 	return __pick_next_timeline(cfs_r_rq);

--