sched: fix overload performance: buddy wakeups

Currently we schedule to the leftmost task in the runqueue. When the
runtimes are very short because of some server/client ping-pong,
especially in over-saturated workloads, this will cycle through all
tasks trashing the cache.

Reduce cache trashing by keeping dependent tasks together by running
newly woken tasks first. However, by not running the leftmost task first
we could starve tasks because the wakee can gain unlimited runtime.

Therefore we only run the wakee if its within a small
(wakeup_granularity) window of the leftmost task. This preserves
fairness, but does alternate server/client task groups.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2008-03-14 21:12:12 +01:00 committed by Ingo Molnar
parent 27d1172660
commit aa2ac25229
2 changed files with 27 additions and 1 deletions

View file

@ -301,7 +301,7 @@ struct cfs_rq {
/* 'curr' points to currently running entity on this cfs_rq.
* It is set to NULL otherwise (i.e when none are currently running).
*/
struct sched_entity *curr;
struct sched_entity *curr, *next;
unsigned long nr_spread_over;

View file

@ -207,6 +207,9 @@ static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
}
}
if (cfs_rq->next == se)
cfs_rq->next = NULL;
rb_erase(&se->run_node, &cfs_rq->tasks_timeline);
}
@ -626,12 +629,32 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
se->prev_sum_exec_runtime = se->sum_exec_runtime;
}
static struct sched_entity *
pick_next(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
s64 diff, gran;
if (!cfs_rq->next)
return se;
diff = cfs_rq->next->vruntime - se->vruntime;
if (diff < 0)
return se;
gran = calc_delta_fair(sysctl_sched_wakeup_granularity, &cfs_rq->load);
if (diff > gran)
return se;
return cfs_rq->next;
}
static struct sched_entity *pick_next_entity(struct cfs_rq *cfs_rq)
{
struct sched_entity *se = NULL;
if (first_fair(cfs_rq)) {
se = __pick_next_entity(cfs_rq);
se = pick_next(cfs_rq, se);
set_next_entity(cfs_rq, se);
}
@ -1070,6 +1093,9 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p)
resched_task(curr);
return;
}
cfs_rq_of(pse)->next = pse;
/*
* Batch tasks do not preempt (their preemption is driven by
* the tick):