Revert "sched/fair: Fix fairness issue on migration"

Mike reported that this recent commit:

  3a47d5124a95 ("sched/fair: Fix fairness issue on migration")

... broke interactivity and the signal starvation test.

We have a proper fix series in the works but ran out of time for
v4.6, so revert the commit.

Reported-by: Mike Galbraith <efault@gmx.de>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 40748dc..e7dd0ec 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3188,25 +3188,17 @@ static inline void check_schedstat_required(void)
 static void
 enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 {
-       bool renorm = !(flags & ENQUEUE_WAKEUP) || (flags & ENQUEUE_WAKING);
-       bool curr = cfs_rq->curr == se;
-
        /*
-        * If we're the current task, we must renormalise before calling
-        * update_curr().
+        * Update the normalized vruntime before updating min_vruntime
+        * through calling update_curr().
         */
-       if (renorm && curr)
+       if (!(flags & ENQUEUE_WAKEUP) || (flags & ENQUEUE_WAKING))
                se->vruntime += cfs_rq->min_vruntime;
 
-       update_curr(cfs_rq);
-
        /*
-        * Otherwise, renormalise after, such that we're placed at the current
-        * moment in time, instead of some random moment in the past.
+        * Update run-time statistics of the 'current'.
         */
-       if (renorm && !curr)
-               se->vruntime += cfs_rq->min_vruntime;
-
+       update_curr(cfs_rq);
        enqueue_entity_load_avg(cfs_rq, se);
        account_entity_enqueue(cfs_rq, se);
        update_cfs_shares(cfs_rq);
@@ -3222,7 +3214,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
                update_stats_enqueue(cfs_rq, se);
                check_spread(cfs_rq, se);
        }
-       if (!curr)
+       if (se != cfs_rq->curr)
                __enqueue_entity(cfs_rq, se);
        se->on_rq = 1;