[PATCH v4 2/6] sched/topology: Introduce sched_group::flags

[Ricardo Neri]

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.

Cc: Aubrey Li <aubrey.li@xxxxxxxxx>
Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Quentin Perret <qperret@xxxxxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Reviewed-by: Len Brown <len.brown@xxxxxxxxx>
Originally-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
Changes since v3:
  * Clear the flags of the scheduling groups of a domain if its child is
    destroyed.
  * Minor rewording of the commit message.

Changes since v2:
  * Introduced this patch.

Changes since v1:
  * N/A
---
 kernel/sched/sched.h    |  1 +
 kernel/sched/topology.c | 21 ++++++++++++++++++---
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index a2c6f6ae6392..fb716e78974d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1799,6 +1799,7 @@ 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 b77ad49dc14f..27c959de175d 100644
--- 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));
-- 
2.17.1