Re: [RFC -v7 PATCH 4/7] Add yield_to(task, preempt) functionality.

Peter Zijlstra
2011-01-31T11:48:13Z

On Wed, 2011-01-26 at 17:21 -0500, Rik van Riel wrote:
> +bool __sched yield_to(struct task_struct *p, bool preempt)
> +{
> + struct task_struct *curr = current;
> + struct rq *rq, *p_rq;
> + unsigned long flags;
> + bool yielded = 0;
> +
> + local_irq_save(flags);
> + rq = this_rq();
> +
> +again:
> + p_rq = task_rq(p);
> + double_rq_lock(rq, p_rq);
> + while (task_rq(p) != p_rq) {
> + double_rq_unlock(rq, p_rq);
> + goto again;
> + }
> +
> + if (!curr->sched_class->yield_to_task)
> + goto out;
> +
> + if (curr->sched_class != p->sched_class)
> + goto out;
> +
> + if (task_running(p_rq, p) || p->state)
> + goto out;
> +
> + yielded = curr->sched_class->yield_to_task(rq, p, preempt);
> +
> +out:
> + double_rq_unlock(rq, p_rq);
> + local_irq_restore(flags);
> +
> + if (yielded)
> + yield();
> +
> + return yielded;
> +}
> +EXPORT_SYMBOL_GPL(yield_to);

yield() will again acquire rq->lock.. not not simply have
->yield_to_task() do everything required and make that an unconditional
schedule()?