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

This reverts commit 5ce74abe788a26698876e66b9c9ce7e7acc25413 (and its
dependent commit 8a5bc075b8d8cf7a87b3f08fad2fba0f5d13295e), because of
audio underruns.

Reported by Rene Herman <rene.herman@keyaccess.nl>, 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 <rene.herman@keyaccess.nl>
Cc: Mike Galbraith <efault@gmx.de>
Acked-by: Con Kolivas <kernel@kolivas.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 18 insertions, 44 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 4c64f85698ae..c13f1bd2df7d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -665,55 +665,13 @@ static int effective_prio(task_t *p)
 }
 
 /*
- * 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++;
@@ -2532,6 +2490,22 @@ unsigned long long current_sched_time(const task_t *tsk)
 }
 
 /*
+ * 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
  * @hardirq_offset: the offset to subtract from hardirq_count()
@@ -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;