Re: bug in Real-Time Preemption

[Michal Schmidt]

Milan Svoboda wrote:
> under non RT preempt:
> (these results are expected)
>
> ./a.out
> Flag: 0, Dif:11714
> ./a.out
> Flag: 0, Dif:11678
>
> under full RT preempt:
> ./a.out
> Flag: 1, Dif:582536
> ./a.out
> Flag: 1, Dif:579791
>
> This shows that thread with bigger priority was
> blocked by the thread with lower priority!

Can you retry with RT-V0.7.48-05 and this patch applied?

Michal
diff -Nurp -X linux-RT/Documentation/dontdiff linux-RT/kernel/sched.c linux-RT.mich/kernel/sched.c
--- linux-RT/kernel/sched.c	2005-06-09 23:09:43.000000000 +0200
+++ linux-RT.mich/kernel/sched.c	2005-06-09 23:29:20.000000000 +0200
@@ -1190,18 +1190,14 @@ out_activate:
 	 * this cpu. Delayed preemption is guaranteed to happen upon
 	 * return to userspace.
 	 */
-	if (cpu != this_cpu) {
+	if (!sync || cpu != this_cpu) {
 		activate_task(p, rq, cpu == this_cpu);
 		if (TASK_PREEMPTS_CURR(p, rq))
 			resched_task(rq->curr);
 	} else {
 		__activate_task(p, rq);
-		if (TASK_PREEMPTS_CURR(p, rq)) {
-			if (sync)
-				set_tsk_need_resched_delayed(rq->curr);
-			else
-				resched_task(rq->curr);
-		}
+		if (TASK_PREEMPTS_CURR(p, rq))
+			set_tsk_need_resched_delayed(rq->curr);
 	}
 	trace_start_sched_wakeup(p, rq);
 	if (rq->curr && p && rq && _need_resched())