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sched: virtual time buddy preemption

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Since we moved wakeup preemption back to virtual time, it makes sense to move
the buddy stuff back as well. The purpose of the buddy scheduling is to allow
a quickly scheduling pair of tasks to run away from the group as far as a
regular busy task would be allowed under wakeup preemption.

This has the advantage that the pair can ping-pong for a while, enjoying
cache-hotness. Without buddy scheduling other tasks would interleave destroying
the cache.

Also, it saves a word in cfs_rq.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra
2008-10-24 11:06:16 +02:00
committed by Ingo Molnar
parent 464b75273f
commit 3f3a490480
2 changed files with 4 additions and 7 deletions
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10
kernel/sched_fair.c
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@@ -791,16 +791,14 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
se->prev_sum_exec_runtime = se->sum_exec_runtime;
}
static int
wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se);
static struct sched_entity *
pick_next(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
struct rq *rq = rq_of(cfs_rq);
u64 pair_slice = rq->clock - cfs_rq->pair_start;
if (!cfs_rq->next || pair_slice > sysctl_sched_min_granularity) {
cfs_rq->pair_start = rq->clock;
if (!cfs_rq->next || wakeup_preempt_entity(cfs_rq->next, se) == 1)
return se;
}
return cfs_rq->next;
}