5 files changed, 90 insertions, 71 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 0542774914d4..4e9fad271c30 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1942,8 +1942,6 @@ int sched_rt_handler(struct ctl_table *table, int write,
                 void __user *buffer, size_t *lenp,
                 loff_t *ppos);
 
-extern unsigned int sysctl_sched_compat_yield;
-
 #ifdef CONFIG_SCHED_AUTOGROUP
 extern unsigned int sysctl_sched_autogroup_enabled;
 
diff --git a/kernel/sched.c b/kernel/sched.c
index 477e1bcc63f9..ae5e1a19b9d6 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -324,7 +324,7 @@ 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, *last;
+        struct sched_entity *curr, *next, *last, *skip;
 
         unsigned int nr_spread_over;
 
diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index eb6cb8edd075..7bacd83a4158 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -179,7 +179,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
 
         raw_spin_lock_irqsave(&rq->lock, flags);
         if (cfs_rq->rb_leftmost)
-                MIN_vruntime = (__pick_next_entity(cfs_rq))->vruntime;
+                MIN_vruntime = (__pick_first_entity(cfs_rq))->vruntime;
         last = __pick_last_entity(cfs_rq);
         if (last)
                 max_vruntime = last->vruntime;
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index a785e08202cf..c0fbeb992833 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -69,14 +69,6 @@ static unsigned int sched_nr_latency = 8;
 unsigned int sysctl_sched_child_runs_first __read_mostly;
 
 /*
- * sys_sched_yield() compat mode
- *
- * This option switches the agressive yield implementation of the
- * old scheduler back on.
- */
-unsigned int __read_mostly sysctl_sched_compat_yield;
-
-/*
  * SCHED_OTHER wake-up granularity.
  * (default: 1 msec * (1 + ilog(ncpus)), units: nanoseconds)
  *
@@ -419,7 +411,7 @@ static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
         rb_erase(&se->run_node, &cfs_rq->tasks_timeline);
 }
 
-static struct sched_entity *__pick_next_entity(struct cfs_rq *cfs_rq)
+static struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
 {
         struct rb_node *left = cfs_rq->rb_leftmost;
 
@@ -429,6 +421,17 @@ static struct sched_entity *__pick_next_entity(struct cfs_rq *cfs_rq)
         return rb_entry(left, struct sched_entity, run_node);
 }
 
+static struct sched_entity *__pick_next_entity(struct sched_entity *se)
+{
+        struct rb_node *next = rb_next(&se->run_node);
+
+        if (!next)
+                return NULL;
+
+        return rb_entry(next, struct sched_entity, run_node);
+}
+
+#ifdef CONFIG_SCHED_DEBUG
 static struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
 {
         struct rb_node *last = rb_last(&cfs_rq->tasks_timeline);
@@ -443,7 +446,6 @@ static struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq)
  * Scheduling class statistics methods:
  */
 
-#ifdef CONFIG_SCHED_DEBUG
 int sched_proc_update_handler(struct ctl_table *table, int write,
                 void __user *buffer, size_t *lenp,
                 loff_t *ppos)
@@ -1017,6 +1019,17 @@ static void __clear_buddies_next(struct sched_entity *se)
         }
 }
 
+static void __clear_buddies_skip(struct sched_entity *se)
+{
+        for_each_sched_entity(se) {
+                struct cfs_rq *cfs_rq = cfs_rq_of(se);
+                if (cfs_rq->skip == se)
+                        cfs_rq->skip = NULL;
+                else
+                        break;
+        }
+}
+
 static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
 {
         if (cfs_rq->last == se)
@@ -1024,6 +1037,9 @@ static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
 
         if (cfs_rq->next == se)
                 __clear_buddies_next(se);
+
+        if (cfs_rq->skip == se)
+                __clear_buddies_skip(se);
 }
 
 static void
@@ -1099,7 +1115,7 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
                 return;
 
         if (cfs_rq->nr_running > 1) {
-                struct sched_entity *se = __pick_next_entity(cfs_rq);
+                struct sched_entity *se = __pick_first_entity(cfs_rq);
                 s64 delta = curr->vruntime - se->vruntime;
 
                 if (delta < 0)
@@ -1143,13 +1159,27 @@ 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);
 
+/*
+ * Pick the next process, keeping these things in mind, in this order:
+ * 1) keep things fair between processes/task groups
+ * 2) pick the "next" process, since someone really wants that to run
+ * 3) pick the "last" process, for cache locality
+ * 4) do not run the "skip" process, if something else is available
+ */
 static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq)
 {
-        struct sched_entity *se = __pick_next_entity(cfs_rq);
+        struct sched_entity *se = __pick_first_entity(cfs_rq);
         struct sched_entity *left = se;
 
-        if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
-                se = cfs_rq->next;
+        /*
+         * Avoid running the skip buddy, if running something else can
+         * be done without getting too unfair.
+         */
+        if (cfs_rq->skip == se) {
+                struct sched_entity *second = __pick_next_entity(se);
+                if (second && wakeup_preempt_entity(second, left) < 1)
+                        se = second;
+        }
 
         /*
          * Prefer last buddy, try to return the CPU to a preempted task.
@@ -1157,6 +1187,12 @@ static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq)
         if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1)
                 se = cfs_rq->last;
 
+        /*
+         * Someone really wants this to run. If it's not unfair, run it.
+         */
+        if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
+                se = cfs_rq->next;
+
         clear_buddies(cfs_rq, se);
 
         return se;
@@ -1333,52 +1369,6 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
         hrtick_update(rq);
 }
 
-/*
- * sched_yield() support is very simple - we dequeue and enqueue.
- *
- * If compat_yield is turned on then we requeue to the end of the tree.
- */
-static void yield_task_fair(struct rq *rq)
-{
-        struct task_struct *curr = rq->curr;
-        struct cfs_rq *cfs_rq = task_cfs_rq(curr);
-        struct sched_entity *rightmost, *se = &curr->se;
-
-        /*
-         * Are we the only task in the tree?
-         */
-        if (unlikely(rq->nr_running == 1))
-                return;
-
-        clear_buddies(cfs_rq, se);
-
-        if (likely(!sysctl_sched_compat_yield) && curr->policy != SCHED_BATCH) {
-                update_rq_clock(rq);
-                /*
-                 * Update run-time statistics of the 'current'.
-                 */
-                update_curr(cfs_rq);
-
-                return;
-        }
-        /*
-         * Find the rightmost entry in the rbtree:
-         */
-        rightmost = __pick_last_entity(cfs_rq);
-        /*
-         * Already in the rightmost position?
-         */
-        if (unlikely(!rightmost || entity_before(rightmost, se)))
-                return;
-
-        /*
-         * Minimally necessary key value to be last in the tree:
-         * Upon rescheduling, sched_class::put_prev_task() will place
-         * 'current' within the tree based on its new key value.
-         */
-        se->vruntime = rightmost->vruntime + 1;
-}
-
 #ifdef CONFIG_SMP
 
 static void task_waking_fair(struct rq *rq, struct task_struct *p)
@@ -1849,6 +1839,14 @@ static void set_next_buddy(struct sched_entity *se)
         }
 }
 
+static void set_skip_buddy(struct sched_entity *se)
+{
+        if (likely(task_of(se)->policy != SCHED_IDLE)) {
+                for_each_sched_entity(se)
+                        cfs_rq_of(se)->skip = se;
+        }
+}
+
 /*
  * Preempt the current task with a newly woken task if needed:
  */
@@ -1947,6 +1945,36 @@ static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
         }
 }
 
+/*
+ * sched_yield() is very simple
+ *
+ * The magic of dealing with the ->skip buddy is in pick_next_entity.
+ */
+static void yield_task_fair(struct rq *rq)
+{
+        struct task_struct *curr = rq->curr;
+        struct cfs_rq *cfs_rq = task_cfs_rq(curr);
+        struct sched_entity *se = &curr->se;
+
+        /*
+         * Are we the only task in the tree?
+         */
+        if (unlikely(rq->nr_running == 1))
+                return;
+
+        clear_buddies(cfs_rq, se);
+
+        if (curr->policy != SCHED_BATCH) {
+                update_rq_clock(rq);
+                /*
+                 * Update run-time statistics of the 'current'.
+                 */
+                update_curr(cfs_rq);
+        }
+
+        set_skip_buddy(se);
+}
+
 #ifdef CONFIG_SMP
 /**************************************************
  * Fair scheduling class load-balancing methods:
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index bc86bb32e126..cbfda7e2416e 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -360,13 +360,6 @@ static struct ctl_table kern_table[] = {
                 .mode           = 0644,
                 .proc_handler   = sched_rt_handler,
         },
-        {
-                .procname       = "sched_compat_yield",
-                .data           = &sysctl_sched_compat_yield,
-                .maxlen         = sizeof(unsigned int),
-                .mode           = 0644,
-                .proc_handler   = proc_dointvec,
-        },
 #ifdef CONFIG_SCHED_AUTOGROUP
         {
                 .procname       = "sched_autogroup_enabled",