Merge branch 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'sched-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  sched: re-tune balancing
  sched: fix buddies for group scheduling
  sched: backward looking buddy
  sched: fix fair preempt check
  sched: cleanup fair task selection

3 files changed, 54 insertions, 29 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index e8819bc6f462..82cc839c9210 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -397,7 +397,7 @@ struct cfs_rq {
          * 'curr' points to currently running entity on this cfs_rq.
          * It is set to NULL otherwise (i.e when none are currently running).
          */
-        struct sched_entity *curr, *next;
+        struct sched_entity *curr, *next, *last;
 
         unsigned long nr_spread_over;
 
@@ -1805,7 +1805,9 @@ task_hot(struct task_struct *p, u64 now, struct sched_domain *sd)
         /*
          * Buddy candidates are cache hot:
          */
-        if (sched_feat(CACHE_HOT_BUDDY) && (&p->se == cfs_rq_of(&p->se)->next))
+        if (sched_feat(CACHE_HOT_BUDDY) &&
+                        (&p->se == cfs_rq_of(&p->se)->next ||
+                         &p->se == cfs_rq_of(&p->se)->last))
                 return 1;
 
         if (p->sched_class != &fair_sched_class)
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index ce514afd78ff..51aa3e102acb 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -341,23 +341,20 @@ static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
                 cfs_rq->rb_leftmost = next_node;
         }
 
-        if (cfs_rq->next == se)
-                cfs_rq->next = NULL;
-
         rb_erase(&se->run_node, &cfs_rq->tasks_timeline);
 }
 
-static inline struct rb_node *first_fair(struct cfs_rq *cfs_rq)
-{
-        return cfs_rq->rb_leftmost;
-}
-
 static struct sched_entity *__pick_next_entity(struct cfs_rq *cfs_rq)
 {
-        return rb_entry(first_fair(cfs_rq), struct sched_entity, run_node);
+        struct rb_node *left = cfs_rq->rb_leftmost;
+
+        if (!left)
+                return NULL;
+
+        return rb_entry(left, struct sched_entity, run_node);
 }
 
-static inline struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
+static struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
 {
         struct rb_node *last = rb_last(&cfs_rq->tasks_timeline);
 
@@ -741,6 +738,12 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int sleep)
 #endif
         }
 
+        if (cfs_rq->last == se)
+                cfs_rq->last = NULL;
+
+        if (cfs_rq->next == se)
+                cfs_rq->next = NULL;
+
         if (se != cfs_rq->curr)
                 __dequeue_entity(cfs_rq, se);
         account_entity_dequeue(cfs_rq, se);
@@ -794,24 +797,15 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
 static int
 wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se);
 
-static struct sched_entity *
-pick_next(struct cfs_rq *cfs_rq, struct sched_entity *se)
-{
-        if (!cfs_rq->next || wakeup_preempt_entity(cfs_rq->next, se) == 1)
-                return se;
-
-        return cfs_rq->next;
-}
-
 static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq)
 {
-        struct sched_entity *se = NULL;
+        struct sched_entity *se = __pick_next_entity(cfs_rq);
 
-        if (first_fair(cfs_rq)) {
-                se = __pick_next_entity(cfs_rq);
-                se = pick_next(cfs_rq, se);
-                set_next_entity(cfs_rq, se);
-        }
+        if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, se) < 1)
+                return cfs_rq->next;
+
+        if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, se) < 1)
+                return cfs_rq->last;
 
         return se;
 }
@@ -1325,26 +1319,53 @@ wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se)
         return 0;
 }
 
+static void set_last_buddy(struct sched_entity *se)
+{
+        for_each_sched_entity(se)
+                cfs_rq_of(se)->last = se;
+}
+
+static void set_next_buddy(struct sched_entity *se)
+{
+        for_each_sched_entity(se)
+                cfs_rq_of(se)->next = se;
+}
+
 /*
  * Preempt the current task with a newly woken task if needed:
  */
 static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int sync)
 {
         struct task_struct *curr = rq->curr;
-        struct cfs_rq *cfs_rq = task_cfs_rq(curr);
         struct sched_entity *se = &curr->se, *pse = &p->se;
 
         if (unlikely(rt_prio(p->prio))) {
+                struct cfs_rq *cfs_rq = task_cfs_rq(curr);
+
                 update_rq_clock(rq);
                 update_curr(cfs_rq);
                 resched_task(curr);
                 return;
         }
 
+        if (unlikely(p->sched_class != &fair_sched_class))
+                return;
+
         if (unlikely(se == pse))
                 return;
 
-        cfs_rq_of(pse)->next = pse;
+        /*
+         * Only set the backward buddy when the current task is still on the
+         * rq. This can happen when a wakeup gets interleaved with schedule on
+         * the ->pre_schedule() or idle_balance() point, either of which can
+         * drop the rq lock.
+         *
+         * Also, during early boot the idle thread is in the fair class, for
+         * obvious reasons its a bad idea to schedule back to the idle thread.
+         */
+        if (sched_feat(LAST_BUDDY) && likely(se->on_rq && curr != rq->idle))
+                set_last_buddy(se);
+        set_next_buddy(pse);
 
         /*
          * We can come here with TIF_NEED_RESCHED already set from new task
@@ -1396,6 +1417,7 @@ static struct task_struct *pick_next_task_fair(struct rq *rq)
 
         do {
                 se = pick_next_entity(cfs_rq);
+                set_next_entity(cfs_rq, se);
                 cfs_rq = group_cfs_rq(se);
         } while (cfs_rq);
 
diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index fda016218296..da5d93b5d2c6 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -12,3 +12,4 @@ SCHED_FEAT(LB_BIAS, 1)
 SCHED_FEAT(LB_WAKEUP_UPDATE, 1)
 SCHED_FEAT(ASYM_EFF_LOAD, 1)
 SCHED_FEAT(WAKEUP_OVERLAP, 0)
+SCHED_FEAT(LAST_BUDDY, 1)