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Date: Tue, 25 Apr 2017 18:26:36 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Lauro Venancio <lvenanci@...hat.com> Cc: lwang@...hat.com, riel@...hat.com, Mike Galbraith <efault@....de>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 4/4] sched/topology: the group balance cpu must be a cpu where the group is installed On Tue, Apr 25, 2017 at 12:56:23PM -0300, Lauro Venancio wrote: > > Another thing I've been thinking about; I think we can do away with the > > kzalloc() in build_group_from_child_sched_domain() and use the sdd->sg > > storage. > I considered this too. I decided to do not change this because I was not > sure if the kzalloc() was there for performance reasons. Currently, all > groups are allocated in the NUMA node they are used. > If we use sdd->sg storage, we may have groups allocated in one NUMA node > being used in another node. Right.. I cannot remember :/ /me once again kicks himself for not writing more comments It does save a few lines.. and I suspect that if we do this, we could actually completely get rid of sched_group_capacity, since its now always the same as the group (again), which should removes more lines still. But I'll shelf this patch for now.. we've got enough changes as is. I still need to write a changelog for the new #2, which has become ugly again, because its needs a second sched_domains_tmpmask. (compile tested only) --- kernel/sched/topology.c | 76 ++++++++++++++++++------------------------------ 1 file changed, 29 insertions(+), 47 deletions(-) --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -501,10 +501,8 @@ enum s_alloc { * balancing. */ static void -build_group_mask(struct sched_domain *sd, struct sched_group *sg, struct cpumask *mask) +build_group_mask(struct sd_data *sdd, struct cpumask *sg_span, struct cpumask *mask) { - const struct cpumask *sg_span = sched_group_cpus(sg); - struct sd_data *sdd = sd->private; struct sched_domain *sibling; int i; @@ -542,49 +540,34 @@ int group_balance_cpu(struct sched_group } static struct sched_group * -build_group_from_child_sched_domain(struct sched_domain *sd, int cpu) +get_overlap_group(struct sd_data *sdd, int cpu) { - struct sched_group *sg; - struct cpumask *sg_span; + struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu); + struct sched_domain *child = sd->child; + struct sched_group *group; + struct cpumask *mask = sched_domains_tmpmask2; - sg = kzalloc_node(sizeof(struct sched_group) + cpumask_size(), - GFP_KERNEL, cpu_to_node(cpu)); + /* + * Overlap must have !overlap children. + * This is before degenerate throws them out. + */ + BUG_ON(!sd->child); - if (!sg) - return NULL; + build_group_mask(sdd, sched_domain_span(child), mask); + cpu = cpumask_first_and(sched_domain_span(child), mask); - sg_span = sched_group_cpus(sg); - if (sd->child) - cpumask_copy(sg_span, sched_domain_span(sd->child)); - else - cpumask_copy(sg_span, sched_domain_span(sd)); + BUG_ON(cpu >= nr_cpu_ids); - return sg; -} + group = *per_cpu_ptr(sdd->sg, cpu); + group->sgc = *per_cpu_ptr(sdd->sgc, cpu); -static void init_overlap_sched_group(struct sched_domain *sd, - struct sched_group *sg) -{ - struct cpumask *mask = sched_domains_tmpmask2; - struct sd_data *sdd = sd->private; - struct cpumask *sg_span; - int cpu; + atomic_inc(&group->ref); + atomic_inc(&group->sgc->ref); - build_group_mask(sd, sg, mask); - cpu = cpumask_first_and(sched_group_cpus(sg), mask); + cpumask_copy(sched_group_cpus(group), sched_domain_span(child)); + cpumask_copy(sched_group_mask(group), mask); - sg->sgc = *per_cpu_ptr(sdd->sgc, cpu); - if (atomic_inc_return(&sg->sgc->ref) == 1) - cpumask_copy(sched_group_mask(sg), mask); - - /* - * Initialize sgc->capacity such that even if we mess up the - * domains and no possible iteration will get us here, we won't - * die on a /0 trap. - */ - sg_span = sched_group_cpus(sg); - sg->sgc->capacity = SCHED_CAPACITY_SCALE * cpumask_weight(sg_span); - sg->sgc->min_capacity = SCHED_CAPACITY_SCALE; + return group; } static int @@ -620,14 +603,18 @@ build_overlap_sched_groups(struct sched_ if (!cpumask_test_cpu(i, sched_domain_span(sibling))) continue; - sg = build_group_from_child_sched_domain(sibling, cpu); - if (!sg) - goto fail; + sg = get_overlap_group(sdd, i); sg_span = sched_group_cpus(sg); cpumask_or(covered, covered, sg_span); - init_overlap_sched_group(sd, sg); + /* + * Initialize sgc->capacity such that even if we mess up the + * domains and no possible iteration will get us here, we won't + * die on a /0 trap. + */ + sg->sgc->capacity = SCHED_CAPACITY_SCALE * cpumask_weight(sg_span); + sg->sgc->min_capacity = SCHED_CAPACITY_SCALE; if (!first) first = sg; @@ -639,11 +626,6 @@ build_overlap_sched_groups(struct sched_ sd->groups = first; return 0; - -fail: - free_sched_groups(first, 0); - - return -ENOMEM; } static int get_group(int cpu, struct sd_data *sdd, struct sched_group **sg)
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