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SubjectRe: [PATCH] sched: enhance the pre/post scheduling logic
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On Wed, 2009-07-29 at 11:08 -0400, Gregory Haskins wrote:

> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 3ab08e4..df14cae 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1045,7 +1045,6 @@ struct sched_class {
> struct rq *busiest, struct sched_domain *sd,
> enum cpu_idle_type idle);
> void (*pre_schedule) (struct rq *this_rq, struct task_struct *task);
> - int (*needs_post_schedule) (struct rq *this_rq);
> void (*post_schedule) (struct rq *this_rq);
> void (*task_wake_up) (struct rq *this_rq, struct task_struct *task);

awesome, one method less ;-)

> +#ifdef CONFIG_SMP
> +
> +/* assumes rq->lock is held */
> +static inline void pre_schedule(struct rq *rq, struct task_struct *prev)
> +{
> + if (prev->sched_class->pre_schedule)
> + prev->sched_class->pre_schedule(rq, prev);
> +}
> +
> +/* rq->lock is NOT held, but preemption is disabled */
> +static inline void post_schedule(struct rq *rq)
> +{
> + if (rq->post_schedule) {
> + unsigned long flags;
> +
> + spin_lock_irqsave(&rq->lock, flags);
> + if (rq->curr->sched_class->post_schedule)
> + rq->curr->sched_class->post_schedule(rq);
> + spin_unlock_irqrestore(&rq->lock, flags);
> +
> + rq->post_schedule = 0;
> + }
> +}
> +
> +#else
>
> - return post_schedule;
> +static inline void pre_schedule(struct rq *rq, struct task_struct *p)
> +{
> +}
> +
> +static inline void post_schedule(struct rq *rq)
> +{
> }
>
> +#endif

Wouldn't you sleep much safer at night if both versions were to check
those assumptions under SCHED_DEBUG? :-)

> @@ -2844,14 +2873,14 @@ asmlinkage void schedule_tail(struct task_struct *prev)
> __releases(rq->lock)
> {
> struct rq *rq = this_rq();
> - int post_schedule;
>
> - post_schedule = finish_task_switch(rq, prev);
> + finish_task_switch(rq, prev);
>
> -#ifdef CONFIG_SMP
> - if (post_schedule)
> - current->sched_class->post_schedule(rq);
> -#endif
> + /*
> + * FIXME: do we need to worry about rq being invalidated by the
> + * task_switch?
> + */
> + post_schedule(rq);
>
> #ifdef __ARCH_WANT_UNLOCKED_CTXSW
> /* In this case, finish_task_switch does not reenable preemption */

You know I really can't take patches with FIXME's in ;-)

I think only switch_to() messes with your stacks, finish_task_switch()
should be safe, but double check me.


OK, so I stuck the patch in anyway..


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