Re: O(1) count_active_tasks()

[Robert Love <rml@tech9.net>]

On Sat, 2002-05-25 at 20:51, William Lee Irwin III wrote:
> rml, I heard you're interested in this, but regardless, here it is.
> AFAICT it computes a faithful load average. Against latest 2.5.18 bk.
> rml, don't worry about stomping on this if you need the counters
> ticking for something else and you can do the same thing(s).

I like.  Very clean.

One question...

>  	rq = task_rq_lock(p, &flags);
> +	if (p->state == TASK_UNINTERRUPTIBLE)
> +		uninterruptible = 1;
>  	p->state = TASK_RUNNING;
>  	if (!p->array) {
> +		if (uninterruptible)
> +			rq->nr_uninterruptible--;
>  		activate_task(p, rq);
>  		if (p->prio < rq->curr->prio)
>  			resched_task(rq->curr);

Why only decrement nr_uninterruptible if it is not already on a
runqueue?  I suspect because then you assume it is a spurious wakeup and
did not have a corresponding deactivate_task?  Same reason we increment
nr_running in activate_task and not here, I suspect... makes sense.

One thought on a quick way to test if the new method is returning
accurate results would be to leave the current count_active_task code
and then add:

	if (nr != (nr_running() + nr_uninterruptible()))
		printk("Danger Will Robinson!\n");

but you probably already did something similar.

	Robert Love