lkml.org 
[lkml]   [2004]   [Nov]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] add requeue task
Con Kolivas wrote:
> add requeue task
>
>
>
> ------------------------------------------------------------------------
>
> 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.
>
> Change the granularity code to requeue tasks at their best priority
> instead of changing priority while they're running. This keeps tasks at
> their top interactive level during their whole timeslice.
>

I wonder... these things are all in sufficiently rarely used places,
that the icache miss might be more costly than the operations saved.

But....
> Signed-off-by: Con Kolivas <kernel@kolivas.org>
>
> Index: linux-2.6.10-rc1-mm2/kernel/sched.c
> ===================================================================
> --- linux-2.6.10-rc1-mm2.orig/kernel/sched.c 2004-11-02 14:48:54.686316718 +1100
> +++ linux-2.6.10-rc1-mm2/kernel/sched.c 2004-11-02 14:52:51.805763544 +1100
> @@ -579,6 +579,16 @@ 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_del(&p->run_list);
> + list_add_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:
> @@ -2425,8 +2435,7 @@ void scheduler_tick(void)
> 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;
> }
> @@ -2467,10 +2476,8 @@ void scheduler_tick(void)
> (p->time_slice >= TIMESLICE_GRANULARITY(p)) &&
> (p->array == rq->active)) {
>
> - dequeue_task(p, rq->active);
> + requeue_task(p, rq->active);
> set_tsk_need_resched(p);
> - p->prio = effective_prio(p);
> - enqueue_task(p, rq->active);
> }
> }
> out_unlock:

This isn't a 1:1 transformation. Looks like the effective_prio there
might be superfluous, but if so that should be a different patch.

> @@ -3569,8 +3576,14 @@ 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
>

Hmm if you have to go to this trouble I'd say its not worth it.
Ingo may want to weigh in though.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 14:07    [from the cache]
©2003-2011 Jasper Spaans