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authorMike Galbraith <efault@gmx.de>2006-04-10 22:52:44 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-04-11 06:18:30 -0700
commit5ce74abe788a26698876e66b9c9ce7e7acc25413 (patch)
tree2e0c2cfc1aad32a9e2903f5e01256f1ed43982e4
parent019ff2d57b0bbe77d1eca19f5b634e5e7ff2a0b8 (diff)
[PATCH] sched: fix interactive task starvation
Fix a starvation problem that occurs when a stream of highly interactive tasks delay an array switch for extended periods despite EXPIRED_STARVING(rq) being true. AFAIKT, the only choice is to enqueue awakening tasks on the expired array in this case. Without this patch, it can be nearly impossible to remotely login to a busy server, and interactive shell commands can starve for minutes. Also, convert the EXPIRED_STARVING macro into an inline function which humans can understand. Signed-off-by: Mike Galbraith <efault@gmx.de> Acked-by: Ingo Molnar <mingo@elte.hu> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Acked-by: Con Kolivas <kernel@kolivas.org> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--kernel/sched.c62
1 files changed, 44 insertions, 18 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index dd153d6f8a0..2e8a146dd06 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -665,13 +665,55 @@ 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 (batch_task(p))
+ if (unlikely(batch_task(p) || expired_starving(rq)))
target = rq->expired;
enqueue_task(p, target);
rq->nr_running++;
@@ -2490,22 +2532,6 @@ 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()
@@ -2640,7 +2666,7 @@ 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;