[PATCH] sched: micro-optimize task requeueing in schedule()

micro-optimize task requeueing in schedule() & clean up recalc_task_prio().

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 12 insertions, 7 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 6e452eb95ac3..a3d1c8e43d34 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -673,7 +673,7 @@ static inline void __activate_idle_task(task_t *p, runqueue_t *rq)
         rq->nr_running++;
 }
 
-static void recalc_task_prio(task_t *p, unsigned long long now)
+static int recalc_task_prio(task_t *p, unsigned long long now)
 {
         /* Caller must always ensure 'now >= p->timestamp' */
         unsigned long long __sleep_time = now - p->timestamp;
@@ -732,7 +732,7 @@ static void recalc_task_prio(task_t *p, unsigned long long now)
                 }
         }
 
-        p->prio = effective_prio(p);
+        return effective_prio(p);
 }
 
 /*
@@ -755,7 +755,7 @@ static void activate_task(task_t *p, runqueue_t *rq, int local)
         }
 #endif
 
-        recalc_task_prio(p, now);
+        p->prio = recalc_task_prio(p, now);
 
         /*
          * This checks to make sure it's not an uninterruptible task
@@ -2751,7 +2751,7 @@ asmlinkage void __sched schedule(void)
         struct list_head *queue;
         unsigned long long now;
         unsigned long run_time;
-        int cpu, idx;
+        int cpu, idx, new_prio;
 
         /*
          * Test if we are atomic.  Since do_exit() needs to call into
@@ -2873,9 +2873,14 @@ go_idle:
                         delta = delta * (ON_RUNQUEUE_WEIGHT * 128 / 100) / 128;
 
                 array = next->array;
-                dequeue_task(next, array);
-                recalc_task_prio(next, next->timestamp + delta);
-                enqueue_task(next, array);
+                new_prio = recalc_task_prio(next, next->timestamp + delta);
+
+                if (unlikely(next->prio != new_prio)) {
+                        dequeue_task(next, array);
+                        next->prio = new_prio;
+                        enqueue_task(next, array);
+                } else
+                        requeue_task(next, array);
         }
         next->activated = 0;
 switch_tasks: