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sched: optimize group load balancer

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I noticed that tg_shares_up() unconditionally takes rq-locks for all cpus
in the sched_domain. This hurts.

We need the rq-locks whenever we change the weight of the per-cpu group sched
entities. To allevate this a little, only change the weight when the new
weight is at least shares_thresh away from the old value.

This avoids the rq-lock for the top level entries, since those will never
be re-weighted, and fuzzes the lower level entries a little to gain performance
in semi-stable situations.

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
2008-10-17 19:27:02 +02:00
committed by Ingo Molnar
parent b0aa51b999
commit ffda12a17a
3 changed files with 36 additions and 20 deletions
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include/linux/sched.h
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@@ -1621,6 +1621,7 @@ extern unsigned int sysctl_sched_features;
extern unsigned int sysctl_sched_migration_cost;
extern unsigned int sysctl_sched_nr_migrate;
extern unsigned int sysctl_sched_shares_ratelimit;
extern unsigned int sysctl_sched_shares_thresh;
int sched_nr_latency_handler(struct ctl_table *table, int write,
struct file *file, void __user *buffer, size_t *length,