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author | Mike Galbraith <efault@gmx.de> | 2006-04-11 07:52:44 +0200 |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-04-11 15:18:30 +0200 |
commit | 5ce74abe788a26698876e66b9c9ce7e7acc25413 (patch) | |
tree | 2e0c2cfc1aad32a9e2903f5e01256f1ed43982e4 /kernel/sched.c | |
parent | [XFS] Fix a problem in aligning inode allocations to stripe unit (diff) | |
download | linux-5ce74abe788a26698876e66b9c9ce7e7acc25413.tar.xz linux-5ce74abe788a26698876e66b9c9ce7e7acc25413.zip |
[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>
Diffstat (limited to 'kernel/sched.c')
-rw-r--r-- | kernel/sched.c | 62 |
1 files changed, 44 insertions, 18 deletions
diff --git a/kernel/sched.c b/kernel/sched.c index dd153d6f8a04..2e8a146dd066 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; |