sched: Add WF_FORK

Avoid the cache buddies from biasing the time distribution away
from fork()ers. Normally the next buddy will be the preferred
scheduling target, but this makes fork()s prefer to run the new
child, whereas we prefer to run the parent, since that will
generate more work.

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

3 files changed, 3 insertions, 2 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 3b07168b6f03..ee1f88993097 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1028,6 +1028,7 @@ struct sched_domain;
  * wake flags
  */
 #define WF_SYNC         0x01            /* waker goes to sleep after wakup */
+#define WF_FORK         0x02            /* child wakeup after fork */
 
 struct sched_class {
         const struct sched_class *next;
diff --git a/kernel/sched.c b/kernel/sched.c
index 4da335cec8ee..0d4c4fea3317 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2602,7 +2602,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
                 inc_nr_running(rq);
         }
         trace_sched_wakeup_new(rq, p, 1);
-        check_preempt_curr(rq, p, 0);
+        check_preempt_curr(rq, p, WF_FORK);
 #ifdef CONFIG_SMP
         if (p->sched_class->task_wake_up)
                 p->sched_class->task_wake_up(rq, p);
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 007958e3c93a..6766959c7f44 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1580,7 +1580,7 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int flags
          */
         if (sched_feat(LAST_BUDDY) && likely(se->on_rq && curr != rq->idle))
                 set_last_buddy(se);
-        if (sched_feat(NEXT_BUDDY))
+        if (sched_feat(NEXT_BUDDY) && !(flags & WF_FORK))
                 set_next_buddy(pse);
 
         /*