sched: Add new wakeup preemption mode: WAKEUP_RUNNING

Create a new wakeup preemption mode, preempt towards tasks that run
shorter on avg. It sets next buddy to be sure we actually run the task
we preempted for.

Test results:

 root@twins:~# while :; do :; done &
 [1] 6537
 root@twins:~# while :; do :; done &
 [2] 6538
 root@twins:~# while :; do :; done &
 [3] 6539
 root@twins:~# while :; do :; done &
 [4] 6540

 root@twins:/home/peter# ./latt -c4 sleep 4
 Entries: 48 (clients=4)

 Averages:
 ------------------------------
        Max          4750 usec
        Avg           497 usec
        Stdev         737 usec

 root@twins:/home/peter# echo WAKEUP_RUNNING > /debug/sched_features

 root@twins:/home/peter# ./latt -c4 sleep 4
 Entries: 48 (clients=4)

 Averages:
 ------------------------------
        Max            14 usec
        Avg             5 usec
        Stdev           3 usec

Disabled by default - needs more testing.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <new-submission>

1 files changed, 11 insertions, 3 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index c741cd9d38de..3e6f78c66876 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1605,9 +1605,6 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
                 return;
         }
 
-        if (!sched_feat(WAKEUP_PREEMPT))
-                return;
-
         if ((sched_feat(WAKEUP_SYNC) && sync) ||
             (sched_feat(WAKEUP_OVERLAP) &&
              (se->avg_overlap < sysctl_sched_migration_cost &&
@@ -1616,6 +1613,17 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
                 return;
         }
 
+        if (sched_feat(WAKEUP_RUNNING)) {
+                if (pse->avg_running < se->avg_running) {
+                        set_next_buddy(pse);
+                        resched_task(curr);
+                        return;
+                }
+        }
+
+        if (!sched_feat(WAKEUP_PREEMPT))
+                return;
+
         find_matching_se(&se, &pse);
 
         BUG_ON(!pse);