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>

1 files changed, 6 insertions, 14 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 40748dc8ea3e..e7dd0ec169be 100644
--- 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;