From: Con Kolivas <kernel@kolivas.org>
We can requeue tasks for cheaper then doing a complete dequeue followed by
an enqueue. Add the requeue_task function and perform it where possible.
This will be hit frequently by upcoming changes to the requeueing in
timeslice granularity.
Signed-off-by: Con Kolivas <kernel@kolivas.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/kernel/sched.c | 22 ++++++++++++++++++----
1 files changed, 18 insertions(+), 4 deletions(-)
diff -puN kernel/sched.c~sched-add_requeue_task kernel/sched.c
--- 25/kernel/sched.c~sched-add_requeue_task 2004-12-03 20:56:31.447979368 -0800
+++ 25-akpm/kernel/sched.c 2004-12-03 20:56:31.454978304 -0800
@@ -601,6 +601,15 @@ static void enqueue_task(struct task_str
}
/*
+ * Put task to the end of the run list without the overhead of dequeue
+ * followed by enqueue.
+ */
+static void requeue_task(struct task_struct *p, prio_array_t *array)
+{
+ list_move_tail(&p->run_list, array->queue + p->prio);
+}
+
+/*
* Used by the migration code - we pull tasks from the head of the
* remote queue so we want these tasks to show up at the head of the
* local queue:
@@ -2349,8 +2358,7 @@ void scheduler_tick(int user_ticks, int
set_tsk_need_resched(p);
/* put it at the end of the queue: */
- dequeue_task(p, rq->active);
- enqueue_task(p, rq->active);
+ requeue_task(p, rq->active);
}
goto out_unlock;
}
@@ -3449,8 +3457,14 @@ asmlinkage long sys_sched_yield(void)
} else if (!rq->expired->nr_active)
schedstat_inc(rq, yld_exp_empty);
- dequeue_task(current, array);
- enqueue_task(current, target);
+ if (array != target) {
+ dequeue_task(current, array);
+ enqueue_task(current, target);
+ } else
+ /*
+ * requeue_task is cheaper so perform that if possible.
+ */
+ requeue_task(current, array);
/*
* Since we are going to call schedule() anyway, there's
_