Re: [RFC PATCH 2/3] sched: add yield_to function

Rik van Riel
2010-12-08T22:59:43Z

On 12/08/2010 03:00 PM, Peter Zijlstra wrote:

> Anyway, complete untested and such..

Looks very promising. I've been making a few changes in the same
direction (except for the fancy CFS bits) and have one way to solve
the one problem you pointed out in your patch.

> +void yield_to(struct task_struct *p)
> +{
...
> + on_rq = p->se.on_rq;
> + if (on_rq)
> + dequeue_task(p_rq, p, 0);
> +
> + ret = 0;
> + if (p->sched_class == curr->sched_class&& curr->sched_class->yield_to)
> + curr->sched_class->yield_to(p);
> +
> + if (on_rq)
> + enqueue_task(p_rq, p, 0);

> diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> index c886717..8689bcd 100644
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c

> +static void yield_to_fair(struct task_stuct *p)
> +{
> + struct sched_entity *se =&current->se;
> + struct sched_entity *p_se =&p->se;
> + u64 lag0, p_lag0;
> + s64 lag, p_lag;
> +
> + lag0 = avg_vruntime(cfs_rq_of(se));
> + p_lag0 = avg_vruntime(cfs_rq_of(p_se));
> +
> + lag = se->vruntime - avg_vruntime(cfs_rq);
> + p_lag = p_se->vruntime - avg_vruntime(p_cfs_rq);
> +
> + if (p_lag> lag) { /* if P is owed less service */
> + se->vruntime = lag0 + p_lag;
> + p_se->vruntime = p_lag + lag;
> + }
> +
> + /*
> + * XXX try something smarter here
> + */
> + resched_task(p);
> + resched_task(current);
> +}

If we do the dequeue_task and enqueue_task here, we can use
check_preempt_curr in yield_to_fair.

Alternatively, we can do the rescheduling from the main
yield_to function, not from yield_to_fair, by calling
check_preempt_curr on p and current after p has been
enqueued.

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