From a5004278f0525dcb9aa43703ef77bf371ea837cd Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 27 Jul 2009 14:04:49 +0200 Subject: [PATCH] sched: Fix cgroup smp fairness Commit ec4e0e2fe018992d980910db901637c814575914 ("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 LKML-Reference: <1248696557.6987.1615.camel@twins> Signed-off-by: Ingo Molnar --- kernel/sched.c | 28 ++++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index ce1056e9b02..26976cd8be0 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -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; } -- 2.46.0