[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>

diff --git a/kernel/sched.c b/kernel/sched.c
index 6e452eb..a3d1c8e 100644 (file)
--- 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: