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

[Ingo Molnar <mingo@elte.hu>]

* Ingo Molnar <mingo@elte.hu> 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.

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.)

	Ingo

--- linux/kernel/sched.c.orig
+++ linux/kernel/sched.c
@@ -2245,10 +2245,10 @@ EXPORT_PER_CPU_SYMBOL(kstat);
  * if a better static_prio task has expired:
  */
 #define EXPIRED_STARVING(rq) \
-	((STARVATION_LIMIT && ((rq)->expired_timestamp && \
+	((task_nice(current) > -20) && ((STARVATION_LIMIT && ((rq)->expired_timestamp && \
 		(jiffies - (rq)->expired_timestamp >= \
 			STARVATION_LIMIT * ((rq)->nr_running) + 1))) || \
-			((rq)->curr->static_prio > (rq)->best_expired_prio))
+			((rq)->curr->static_prio > (rq)->best_expired_prio)))
 
 /*
  * Do the virtual cpu time signal calculations.
@@ -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)