On 04/24/2017 11:27 AM, Peter Zijlstra wrote:
> 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)
Yes, it has the same result. I duplicated the build_group_mask magic to
avoid building the complete mask for all instances of a group.
Currently, the mask is built just once per group.
>>
>> ---
>> --- 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
