Re: [2.6.16-rc6 patch] fix interactive task starvation

[Andrew Morton <akpm@osdl.org>]

Mike Galbraith <efault@gmx.de> wrote:
>
> On Fri, 2006-03-17 at 22:22 -0800, Andrew Morton wrote:
> > Mike Galbraith <efault@gmx.de> wrote:
> > >
> > > > Does this have to be a macro?
> > > > 
> > > 
> > > I suppose not, now inlined.
> > > 
> > 
> > It would be nice to uninline the function and then to modify it in a
> > followup patch.  That way, we get to see what changed, which is one of the
> > reasons to not use megamacros (sorry).
> 
> Ok, take 3 below, with updated main comment as well.
> 

Thanks for doing that.  Not really your job, but someone has to do these
things ;)

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

You can't trick me that easily - I kept a copy of your changlog!

>  /*
> + * We place interactive tasks back into the active array, if possible.
> + *
> + * To guarantee that this does not starve expired tasks we ignore the
> + * interactivity of a task if the first expired task had to wait more
> + * than a 'reasonable' amount of time. This deadline timeout is
> + * load-dependent, as the frequency of array switched decreases with
> + * increasing number of running tasks. We also ignore the interactivity
> + * if a better static_prio task has expired, and switch periodically
> + * regardless, to ensure that highly interactive tasks do not starve
> + * the less fortunate for unreasonably long periods.
> + */
> +static int expired_starving(runqueue_t *rq)

I'll make that inline..

> +{
> +	int limit;
> +
> +	/*
> +	 * Arrays were recently switched, all is well.
> +	 */
> +	if (!rq->expired_timestamp)
> +		return 0;
> +
> +	limit = STARVATION_LIMIT * rq->nr_running;

In the previous iteration you had, effectively,

	if (!limit)
		return 0;

in here.   But it's now gone.   Deliberate?
	
> +	/*
> +	 * It's time to switch arrays.
> +	 */
> +	if (jiffies - rq->expired_timestamp >= limit)
> +		return 1;
> +
> +	/*
> +	 * There's a better selection in the expired array.
> +	 */
> +	if (rq->curr->static_prio > rq->best_expired_prio)
> +		return 1;
> +
> +	/*
> +	 * All is well.
> +	 */
> +	return 0;
> +}