Re: [ck] Re: SD still better than CFS for 3d ?(was Re: 2.6.23-rc1)

Ingo Molnar
2007-07-30T18:38:40Z

* Miguel Figueiredo <elmig@debianpt.org> wrote:

> in mainline (2.6.22):
> /**
> * sys_sched_yield - yield the current processor to other threads.
> *
> * This function yields the current CPU by moving the calling thread
> * to the expired array. If there are no other threads running on this
> * CPU then this function will return.
> */
>
> you changed it to something like:
>
> if (unlikely(rq->nr_running == 1))
> schedstat_inc(rq, yld_act_empty);
> else
> current->sched_class->yield_task(rq, current);
>
> wile mainline (2.6.22) and SD use:
>
> dequeue_task(current, array);
> enqueue_task(current, target);

this is what CFS does:

static void yield_task_fair(struct rq *rq, struct task_struct *p)
{
struct cfs_rq *cfs_rq = task_cfs_rq(p);
u64 now = __rq_clock(rq);

/*
* Dequeue and enqueue the task to update its
* position within the tree:
*/
dequeue_entity(cfs_rq, &p->se, 0, now);
enqueue_entity(cfs_rq, &p->se, 0, now);
}

Ingo