Re: 2.6.0 schedule_tick question

[Davide Libenzi <davidel@xmailserver.org>]

On Sat, 10 Jan 2004, Der Herr Hofrat wrote:

>  in 2.6.0 kernel/sched.c scheduler_tick currently the 
>  case of rt_tasks for SCHED_RR is doing
> 
> 	if ((p->policy == SCHED_RR) && !--p->time_slice) {
> 			...
>                         dequeue_task(p, rq->active);
>                         enqueue_task(p, rq->active);
> 
>  which is:
> 
> static inline void dequeue_task(struct task_struct *p, prio_array_t *array)
> {
>         array->nr_active--;
>         list_del(&p->run_list);
>         if (list_empty(array->queue + p->prio))
>                 __clear_bit(p->prio, array->bitmap);
> }
> 
> static inline void enqueue_task(struct task_struct *p, prio_array_t *array)
> {
>         list_add_tail(&p->run_list, array->queue + p->prio);
>         __set_bit(p->prio, array->bitmap);
>         array->nr_active++;
>         p->array = array;
> }
> 
>  looking at these two functions this looks like quite some overhead as it
>  actually could be reduced to:
> 
>         list_del(&p->run_list);
> 	list_add_tail(&p->run_list, array->queue + p->prio);
> 
>  for the rest I don't see any effect it would have ?

Yes, we could have a rotate_task() function but the impact is basically 
zero because of the little overhead compared to the frequency of the 
operation.



- Davide