sched: Remove avg_overlap

Both avg_overlap and avg_wakeup had an inherent problem in that their accuracy
was detrimentally affected by cross-cpu wakeups, this because we are missing
the necessary call to update_curr().  This can't be fixed without increasing
overhead in our already too fat fastpath.

Additionally, with recent load balancing changes making us prefer to place tasks
in an idle cache domain (which is good for compute bound loads), communicating
tasks suffer when a sync wakeup, which would enable affine placement, is turned
into a non-sync wakeup by SYNC_LESS.  With one task on the runqueue, wake_affine()
rejects the affine wakeup request, leaving the unfortunate where placed, taking
frequent cache misses.

Remove it, and recover some fastpath cycles.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1268301121.6785.30.camel@marge.simson.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 0 insertions, 18 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 6fc62854422c..c3b69d4b5d65 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1241,7 +1241,6 @@ static inline unsigned long effective_load(struct task_group *tg, int cpu,
 
 static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
 {
-        struct task_struct *curr = current;
         unsigned long this_load, load;
         int idx, this_cpu, prev_cpu;
         unsigned long tl_per_task;
@@ -1256,18 +1255,6 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
         load      = source_load(prev_cpu, idx);
         this_load = target_load(this_cpu, idx);
 
-        if (sync) {
-               if (sched_feat(SYNC_LESS) &&
-                   (curr->se.avg_overlap > sysctl_sched_migration_cost ||
-                    p->se.avg_overlap > sysctl_sched_migration_cost))
-                       sync = 0;
-        } else {
-                if (sched_feat(SYNC_MORE) &&
-                    (curr->se.avg_overlap < sysctl_sched_migration_cost &&
-                     p->se.avg_overlap < sysctl_sched_migration_cost))
-                        sync = 1;
-        }
-
         /*
          * If sync wakeup then subtract the (maximum possible)
          * effect of the currently running task from the load
@@ -1711,11 +1698,6 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
         if (sched_feat(WAKEUP_SYNC) && sync)
                 goto preempt;
 
-        if (sched_feat(WAKEUP_OVERLAP) &&
-                        se->avg_overlap < sysctl_sched_migration_cost &&
-                        pse->avg_overlap < sysctl_sched_migration_cost)
-                goto preempt;
-
         if (!sched_feat(WAKEUP_PREEMPT))
                 return;