Re: [2.6.16-mm1 patch] throttling tree patches

[Con Kolivas <kernel@kolivas.org>]

On Friday 24 March 2006 22:03, Mike Galbraith wrote:
> Greetings,

/me waves

> Ignore timewarps caused by SMP timestamp rounding.  Also, don't stamp a
> task with a computed timestamp, stamp with the already called clock.

Looks good. Actually now < p->timestamp is not going to only happen on SMP. 
Once every I don't know how often the sched_clock seems to return a value 
that appears to have been in the past (I believe Peter has instrumented 
this).

> Signed-off-by: Mike Galbraith <efault@gmx.de>

> +		__sleep_time = 0ULL;

I don't think the ULL is necessary.

> -	unsigned long long now;
> +	unsigned long long now, comp;
>
> -	now = sched_clock();
> +	now = comp = sched_clock();
>  #ifdef CONFIG_SMP
>  	if (!local) {
>  		/* Compensate for drifting sched_clock */
>  		runqueue_t *this_rq = this_rq();
> -		now = (now - this_rq->timestamp_last_tick)
> +		comp = (now - this_rq->timestamp_last_tick)
>  			+ rq->timestamp_last_tick;
>  	}
>  #endif
>
>  	if (!rt_task(p))
> -		p->prio = recalc_task_prio(p, now);
> +		p->prio = recalc_task_prio(p, comp);

Seems wasteful of a very expensive (on 32bit) unsigned long long on 
uniprocessor builds.

Cheers,
Con