Re: [PATCH] [request for inclusion] Realtime LSM

[Jack O'Quin]

Ingo Molnar <mingo@xxxxxxx> writes:

> * Ingo Molnar <mingo@xxxxxxx> wrote:
>
>> i'm not suggesting that this is the way to go, it's just to test how
>> nice--20 tasks would perform (on the hacked kernel). We still dont
>> have this data, because in the other tests you tried, some
>> non-highprio threads got nice--20 priority as well, which can (and
>> apparently do) interfere with the highprio threads.

I could hack the threads that the test actually uses just to get some
numbers.  But, that will break some existing JACK clients.

> ('highprio threads' are the ones that normally get SCHED_FIFO priority
> with -R, 'lowprio threads' are the other client-side threads, if any.)

I usually call them `realtime threads' and `non-realtime threads'.
Means the same thing.  I think of them that way, because any code
running in a realtime thread is severely constrained.  It must be
written *very* carefully, almost like a hardware interrupt handler.

> to make it easier to test, i've written an API hack: with the kernel
> patch below setscheduler() will set the task to nice --20 if you use
> SCHED_FIFO and sched_priority of 1. I.e. all you need to do is to run
> Jack with -R and use an RT priority of 1 - all the highprio threads
> should then become nice --20. If you use RT prio 2 (or higher) it should
> be SCHED_FIFO again. Just apply the patch to 2.6.11-rc1 (2.6.10 might
> work too) and it will work automatically. (the hack also includes the
> earlier 'no starvation for nice--20 tasks' hack.)

Good idea, thanks.

These tests mean a lot more running "real" audio programs.  :-)

> @@ -3211,6 +3211,12 @@ static inline task_t *find_process_by_pi
>  static void __setscheduler(struct task_struct *p, int policy, int prio)
>  {
>  	BUG_ON(p->array);
> +	if (prio == 1 && policy != SCHED_NORMAL) {
> +		p->policy = SCHED_NORMAL;
> +		p->static_prio = NICE_TO_PRIO(-20);
> +		p->prio = p->static_prio;
> +		return;
> +	}
>  	p->policy = policy;
>  	p->rt_priority = prio;
>  	if (policy != SCHED_NORMAL)
>

JACK actually uses three different priorities, the defaults are 9, 10
and 20.  How about if I change this test?

	if (prio <= 20 && policy != SCHED_NORMAL) {

Or, should that be?

	if (prio > 0 && prio <= 20 && policy != SCHED_NORMAL) {
-- 
  joq
-
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