Revert "[PATCH] sched: fix interactive task starvation"

This reverts commit 5ce74ab (and its
dependent commit 8a5bc07), because of
audio underruns.

Reported by Rene Herman <[email protected]>, who also pinpointed
the exact cause of the underruns:

  "Audio underruns galore, with only ogg123 and firefox (browsing the
   GIT tree online is also a nice trigger by the way).

   If I back it out, everything is fine for me again."

Cc: Rene Herman <[email protected]>
Cc: Mike Galbraith <[email protected]>
Acked-by: Con Kolivas <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: Linus Torvalds

kernel/sched.c

@@ -664,56 +664,14 @@ static int effective_prio(task_t *p)
 	return prio;
 }
 
-/*
- * 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 inline int expired_starving(runqueue_t *rq)
-{
-	int limit;
-
-	/*
-	 * Arrays were recently switched, all is well
-	 */
-	if (!rq->expired_timestamp)
-		return 0;
-
-	limit = STARVATION_LIMIT * rq->nr_running;
-
-	/*
-	 * 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;
-}
-
 /*
  * __activate_task - move a task to the runqueue.
  */
 static void __activate_task(task_t *p, runqueue_t *rq)
 {
 	prio_array_t *target = rq->active;
 
-	if (unlikely(batch_task(p) || (expired_starving(rq) && !rt_task(p))))
+	if (batch_task(p))
 		target = rq->expired;
 	enqueue_task(p, target);
 	rq->nr_running++;
@@ -2531,6 +2489,22 @@ unsigned long long current_sched_time(const task_t *tsk)
 	return ns;
 }
 
+/*
+ * 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:
+ */
+#define EXPIRED_STARVING(rq) \
+	((STARVATION_LIMIT && ((rq)->expired_timestamp && \
+		(jiffies - (rq)->expired_timestamp >= \
+			STARVATION_LIMIT * ((rq)->nr_running) + 1))) || \
+			((rq)->curr->static_prio > (rq)->best_expired_prio))
+
 /*
  * Account user cpu time to a process.
  * @p: the process that the cpu time gets accounted to
@@ -2666,7 +2640,7 @@ void scheduler_tick(void)
 
 		if (!rq->expired_timestamp)
 			rq->expired_timestamp = jiffies;
-		if (!TASK_INTERACTIVE(p) || expired_starving(rq)) {
+		if (!TASK_INTERACTIVE(p) || EXPIRED_STARVING(rq)) {
 			enqueue_task(p, rq->expired);
 			if (p->static_prio < rq->best_expired_prio)
 				rq->best_expired_prio = p->static_prio;