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sched: add avg_overlap decay

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Impact: more precise avg_overlap metric - better load-balancing

avg_overlap is used to measure the runtime overlap of the waker and
wakee.

However, when a process changes behaviour, eg a pipe becomes
un-congested and we don't need to go to sleep after a wakeup
for a while, the avg_overlap value grows stale.

When running we use the avg runtime between preemption as a
measure for avg_overlap since the amount of runtime can be
correlated to cache footprint.

The longer we run, the less likely we'll be wanting to be
migrated to another CPU.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1236709131.25234.576.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Mike Galbraith 2009-03-10 19:08:11 +01:00 committed by Ingo Molnar
parent 57310a98a3
commit df1c99d416
1 changed files with 23 additions and 1 deletions
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24
kernel/sched.c
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@ -4620,6 +4620,28 @@ static inline void schedule_debug(struct task_struct *prev)
#endif
}
static void put_prev_task(struct rq *rq, struct task_struct *prev)
{
if (prev->state == TASK_RUNNING) {
u64 runtime = prev->se.sum_exec_runtime;
runtime -= prev->se.prev_sum_exec_runtime;
runtime = min_t(u64, runtime, 2*sysctl_sched_migration_cost);
/*
* In order to avoid avg_overlap growing stale when we are
* indeed overlapping and hence not getting put to sleep, grow
* the avg_overlap on preemption.
*
* We use the average preemption runtime because that
* correlates to the amount of cache footprint a task can
* build up.
*/
update_avg(&prev->se.avg_overlap, runtime);
}
prev->sched_class->put_prev_task(rq, prev);
}
/*
* Pick up the highest-prio task:
*/
@ -4698,7 +4720,7 @@ need_resched_nonpreemptible:
if (unlikely(!rq->nr_running))
idle_balance(cpu, rq);
prev->sched_class->put_prev_task(rq, prev);
put_prev_task(rq, prev);
next = pick_next_task(rq);
if (likely(prev != next)) {