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Commit a5004278 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: Fix cgroup smp fairness 



Commit ec4e0e2f ("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: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1248696557.6987.1615.camel@twins>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 8e9ed8b0

kernel/sched.c

+20 −8
Original line number Diff line number Diff line
@@ -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;

}