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SubjectRe: [PATCH 4/4] sched/topology: the group balance cpu must be a cpu where the group is installed
On Mon, Apr 24, 2017 at 04:19:44PM +0200, Peter Zijlstra wrote:
> On Mon, Apr 24, 2017 at 03:03:26PM +0200, Peter Zijlstra wrote:
>
> > Also, would it not make sense to re-order patch 2 to come after this,
> > such that we _do_ have the group_mask available and don't have to jump
> > through hoops in order to link up the sgc? Afaict we don't actually use
> > the sgc until the above (reverse) loop computing the CPU capacities.
>
> That is, if I force 4 on without 2, then doesn't something like the
> below also do the right thing? (without duplicating part of the magic
> already contained in build_group_mask)
>
> ---
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -498,13 +498,16 @@ enum s_alloc {
> *
> * This function can only be used when all the groups are already built.
> */
> -static void build_group_mask(struct sched_domain *sd, struct sched_group *sg)
> +static void
> +build_group_mask(struct sched_domain *sd, struct sched_group *sg, struct cpumask *mask)
> {
> const struct cpumask *sg_span = sched_group_cpus(sg);
> struct sd_data *sdd = sd->private;
> struct sched_domain *sibling;
> int i;
>
> + cpumask_clear(mask);
> +
> for_each_cpu(i, sg_span) {
> sibling = *per_cpu_ptr(sdd->sd, i);
>
> @@ -514,7 +517,7 @@ static void build_group_mask(struct sche
> if (!cpumask_equal(sg_span, sched_group_cpus(sibling->groups)))
> continue;
>
> - cpumask_set_cpu(i, sched_group_mask(sg));
> + cpumask_set_cpu(i, mask);
> }
> }
>
> @@ -549,14 +552,19 @@ build_group_from_child_sched_domain(stru
> }
>
> static void init_overlap_sched_group(struct sched_domain *sd,
> - struct sched_group *sg, int cpu)
> + struct sched_group *sg)
> {
> + struct cpumask *mask = sched_domains_tmpmask;
> struct sd_data *sdd = sd->private;
> struct cpumask *sg_span;
> + int cpu;
> +
> + build_group_mask(sd, sg, mask);
> + cpu = cpumask_first_and(sched_group_mask(sg), mask); /* balance cpu */

s/group_mask/group_span/

>
> sg->sgc = *per_cpu_ptr(sdd->sgc, cpu);
> if (atomic_inc_return(&sg->sgc->ref) == 1)
> - build_group_mask(sd, sg);
> + cpumask_copy(sched_group_mask(sg), mask);
>
> /*
> * Initialize sgc->capacity such that even if we mess up the

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