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sched: Fix cgroup smp fairness

Browse source 
Commit ec4e0e2fe0 ("fix
inconsistency when redistribute per-cpu tg->cfs_rq shares")
broke cgroup smp fairness.

In order to avoid starvation of newly placed tasks, we never
quite set the share of an empty cpu group-task to 0, but
instead we set it as if there's a single NICE-0 task present.

If however we actually set this in cfs_rq[cpu]->shares, that
means the total shares for that group will be slightly inflated
every time we balance, causing the observed unfairness.

Fix this by setting cfs_rq[cpu]->shares to 0 but actually
setting the effective weight of the related se to the inflated
number.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1248696557.6987.1615.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-07-27 14:04:49 +02:00 committed by Ingo Molnar
parent 8e9ed8b024
commit a5004278f0
1 changed files with 20 additions and 8 deletions
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28
kernel/sched.c
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@ -1523,13 +1523,18 @@ static void
update_group_shares_cpu(struct task_group *tg, int cpu,
unsigned long sd_shares, unsigned long sd_rq_weight)
{
unsigned long shares;
unsigned long rq_weight;
unsigned long shares;
int boost = 0;
if (!tg->se[cpu])
return;
rq_weight = tg->cfs_rq[cpu]->rq_weight;
if (!rq_weight) {
boost = 1;
rq_weight = NICE_0_LOAD;
}
/*
* \Sum shares * rq_weight
@ -1546,8 +1551,7 @@ update_group_shares_cpu(struct task_group *tg, int cpu,
unsigned long flags;
spin_lock_irqsave(&rq->lock, flags);
tg->cfs_rq[cpu]->shares = shares;
tg->cfs_rq[cpu]->shares = boost ? 0 : shares;
__set_se_shares(tg->se[cpu], shares);
spin_unlock_irqrestore(&rq->lock, flags);
}
@ -1560,7 +1564,7 @@ update_group_shares_cpu(struct task_group *tg, int cpu,
*/
static int tg_shares_up(struct task_group *tg, void *data)
{
unsigned long weight, rq_weight = 0;
unsigned long weight, rq_weight = 0, eff_weight = 0;
unsigned long shares = 0;
struct sched_domain *sd = data;
int i;
@ -1572,11 +1576,13 @@ static int tg_shares_up(struct task_group *tg, void *data)
* run here it will not get delayed by group starvation.
*/
weight = tg->cfs_rq[i]->load.weight;
tg->cfs_rq[i]->rq_weight = weight;
rq_weight += weight;
if (!weight)
weight = NICE_0_LOAD;
tg->cfs_rq[i]->rq_weight = weight;
rq_weight += weight;
eff_weight += weight;
shares += tg->cfs_rq[i]->shares;
}
@ -1586,8 +1592,14 @@ static int tg_shares_up(struct task_group *tg, void *data)
if (!sd->parent || !(sd->parent->flags & SD_LOAD_BALANCE))
shares = tg->shares;
for_each_cpu(i, sched_domain_span(sd))
update_group_shares_cpu(tg, i, shares, rq_weight);
for_each_cpu(i, sched_domain_span(sd)) {
unsigned long sd_rq_weight = rq_weight;
if (!tg->cfs_rq[i]->rq_weight)
sd_rq_weight = eff_weight;
update_group_shares_cpu(tg, i, shares, sd_rq_weight);
}
return 0;
}