Re: [PATCH] sched: activate SCHED BATCH expired

[Nick Piggin]

Con Kolivas wrote:

> Ok here's a patch that does exactly that. Without an "inline" hint, gcc 4.1.0
> chooses not to inline this function. I can't say I have a strong opinion
> about whether it should be inlined or not (93 bytes larger inlined), so I've
> decided not to given the current trend.

Sigh, sacrifice for the common case! :P


> Index: linux-2.6.16-rc6-mm1/kernel/sched.c
> ===================================================================
> --- linux-2.6.16-rc6-mm1.orig/kernel/sched.c	2006-03-13 20:12:15.000000000 +1100
> +++ linux-2.6.16-rc6-mm1/kernel/sched.c	2006-03-17 23:08:12.000000000 +1100
> @@ -737,9 +737,12 @@ static inline void dec_nr_running(task_t
>  /*
>   * __activate_task - move a task to the runqueue.
>   */
> -static inline void __activate_task(task_t *p, runqueue_t *rq)
> +static void __activate_task(task_t *p, runqueue_t *rq)
>  {
> -	enqueue_task(p, rq->active);
> +	if (batch_task(p))
> +		enqueue_task(p, rq->expired);
> +	else
> +		enqueue_task(p, rq->active);
>  	inc_nr_running(p, rq);
>  }
>  

I prefer:

  prio_array_t *target = rq->active;
  if (batch_task(p))
    target = rq->expired;
  enqueue_task(p, target);

Because gcc can use things like predicated instructions for it.
But perhaps it is smart enough these days to recognise this?
At least in the past I have seen it start using cmov after doing
such a conversion.

At any rate, I think it looks nicer as well. IMO, of course.

--
SUSE Labs, Novell Inc.
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