sched: rework enqueue/dequeue_entity() to get rid of set_curr_task()

rework enqueue/dequeue_entity() to get rid of 
sched_class::set_curr_task(). This simplifies sched_setscheduler(), 
rt_mutex_setprio() and sched_move_tasks().

   text    data     bss     dec     hex filename
  24330    2734      20   27084    69cc sched.o.before
  24233    2730      20   26983    6967 sched.o.after

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 25 insertions, 30 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 4dd256d46853..568e922255c6 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -472,9 +472,20 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
 }
 
 static void
-enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int wakeup)
+enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
+                int wakeup, int set_curr)
 {
         /*
+         * In case of the 'current'.
+         */
+        if (unlikely(set_curr)) {
+                update_stats_curr_start(cfs_rq, se);
+                cfs_rq->curr = se;
+                account_entity_enqueue(cfs_rq, se);
+                return;
+        }
+
+        /*
          * Update the fair clock.
          */
         update_curr(cfs_rq);
@@ -485,8 +496,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int wakeup)
         }
 
         update_stats_enqueue(cfs_rq, se);
-        if (se != cfs_rq->curr)
-                __enqueue_entity(cfs_rq, se);
+        __enqueue_entity(cfs_rq, se);
         account_entity_enqueue(cfs_rq, se);
 }
 
@@ -506,8 +516,12 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int sleep)
                 }
         }
 #endif
-        if (se != cfs_rq->curr)
+        if (likely(se != cfs_rq->curr))
                 __dequeue_entity(cfs_rq, se);
+        else {
+                update_stats_curr_end(cfs_rq, se);
+                cfs_rq->curr = NULL;
+        }
         account_entity_dequeue(cfs_rq, se);
 }
 
@@ -689,12 +703,17 @@ static void enqueue_task_fair(struct rq *rq, struct task_struct *p, int wakeup)
 {
         struct cfs_rq *cfs_rq;
         struct sched_entity *se = &p->se;
+        int set_curr = 0;
+
+        /* Are we enqueuing the current task? */
+        if (unlikely(task_running(rq, p)))
+                set_curr = 1;
 
         for_each_sched_entity(se) {
                 if (se->on_rq)
                         break;
                 cfs_rq = cfs_rq_of(se);
-                enqueue_entity(cfs_rq, se, wakeup);
+                enqueue_entity(cfs_rq, se, wakeup, set_curr);
         }
 }
 
@@ -742,7 +761,7 @@ static void yield_task_fair(struct rq *rq)
                  * position within the tree:
                  */
                 dequeue_entity(cfs_rq, se, 0);
-                enqueue_entity(cfs_rq, se, 0);
+                enqueue_entity(cfs_rq, se, 0, 1);
 
                 return;
         }
@@ -985,29 +1004,6 @@ static void task_new_fair(struct rq *rq, struct task_struct *p)
         resched_task(rq->curr);
 }
 
-#ifdef CONFIG_FAIR_GROUP_SCHED
-/* Account for a task changing its policy or group.
- *
- * This routine is mostly called to set cfs_rq->curr field when a task
- * migrates between groups/classes.
- */
-static void set_curr_task_fair(struct rq *rq)
-{
-        struct sched_entity *se = &rq->curr->se;
-
-        for_each_sched_entity(se)
-                set_next_entity(cfs_rq_of(se), se);
-}
-#else
-static void set_curr_task_fair(struct rq *rq)
-{
-        struct sched_entity *se = &rq->curr->se;
-        struct cfs_rq *cfs_rq = cfs_rq_of(se);
-
-        cfs_rq->curr = se;
-}
-#endif
-
 /*
  * All the scheduling class methods:
  */
@@ -1023,7 +1019,6 @@ struct sched_class fair_sched_class __read_mostly = {
 
         .load_balance           = load_balance_fair,
 
-        .set_curr_task          = set_curr_task_fair,
         .task_tick              = task_tick_fair,
         .task_new               = task_new_fair,
 };