sched/topology: Introduce sched_group::flags

There exist situations in which the load balance needs to know the
properties of the CPUs in a scheduling group. When using asymmetric
packing, for instance, the load balancer needs to know not only the
state of dst_cpu but also of its SMT siblings, if any.

Use the flags of the child scheduling domains to initialize scheduling
group flags. This will reflect the properties of the CPUs in the
group.

A subsequent changeset will make use of these new flags. No functional
changes are introduced.

Originally-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Reviewed-by: Len Brown <len.brown@intel.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20210911011819.12184-3-ricardo.neri-calderon@linux.intel.com

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 198058b..e5c4d4d 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1808,6 +1808,7 @@ struct sched_group {
        unsigned int            group_weight;
        struct sched_group_capacity *sgc;
        int                     asym_prefer_cpu;        /* CPU of highest priority in group */
+       int                     flags;
 
        /*
         * The CPUs this group covers.

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 4e8698e..c56faae 100644 (file)
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -716,8 +716,20 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
                tmp = sd;
                sd = sd->parent;
                destroy_sched_domain(tmp);
-               if (sd)
+               if (sd) {
+                       struct sched_group *sg = sd->groups;
+
+                       /*
+                        * sched groups hold the flags of the child sched
+                        * domain for convenience. Clear such flags since
+                        * the child is being destroyed.
+                        */
+                       do {
+                               sg->flags = 0;
+                       } while (sg != sd->groups);
+
                        sd->child = NULL;
+               }
        }
 
        for (tmp = sd; tmp; tmp = tmp->parent)
@@ -916,10 +928,12 @@ build_group_from_child_sched_domain(struct sched_domain *sd, int cpu)
                return NULL;
 
        sg_span = sched_group_span(sg);
-       if (sd->child)
+       if (sd->child) {
                cpumask_copy(sg_span, sched_domain_span(sd->child));
-       else
+               sg->flags = sd->child->flags;
+       } else {
                cpumask_copy(sg_span, sched_domain_span(sd));
+       }
 
        atomic_inc(&sg->ref);
        return sg;
@@ -1169,6 +1183,7 @@ static struct sched_group *get_group(int cpu, struct sd_data *sdd)
        if (child) {
                cpumask_copy(sched_group_span(sg), sched_domain_span(child));
                cpumask_copy(group_balance_mask(sg), sched_group_span(sg));
+               sg->flags = child->flags;
        } else {
                cpumask_set_cpu(cpu, sched_group_span(sg));
                cpumask_set_cpu(cpu, group_balance_mask(sg));