[PATCH v3 4/6] sched/fair: Carve out logic to mark a group for asymmetric packing

[Ricardo Neri]

Currently when balancing load, a candidate busiest group is marked for
asymmetric packing if, among other factors, dst_cpu has higher priority
than the preferred CPU of the candidate busiest group. However, other
factors influence the decision, such as the state of the SMT siblings of
dst_cpu, if any.

Thus, create a separate function, sched_asym(), in which logic for such
decisions can be implemented. A subsequent changeset will introduce logic
to deal with SMT.

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: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Quentin Perret <qperret@xxxxxxxxxx>
Cc: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Co-developed-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 v2:
  * Introduced this patch.

Changes since v1:
  * N/A
---
 kernel/sched/fair.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c8c04e9d0d3b..c8b66a5d593e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8447,6 +8447,20 @@ group_type group_classify(unsigned int imbalance_pct,
 	return group_has_spare;
 }
 
+static inline bool
+sched_asym(struct lb_env *env, struct sd_lb_stats *sds,  struct sg_lb_stats *sgs,
+	   struct sched_group *group)
+{
+	/*
+	 * Because sd->groups starts with the local group, anything that isn't
+	 * the local group will have access to the local state.
+	 */
+	if (group == sds->local)
+		return false;
+
+	return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu);
+}
+
 /**
  * update_sg_lb_stats - Update sched_group's statistics for load balancing.
  * @env: The load balancing environment.
@@ -8507,18 +8521,17 @@ static inline void update_sg_lb_stats(struct lb_env *env,
 		}
 	}
 
+	sgs->group_capacity = group->sgc->capacity;
+
+	sgs->group_weight = group->group_weight;
+
 	/* Check if dst CPU is idle and preferred to this group */
 	if (!local_group && env->sd->flags & SD_ASYM_PACKING &&
-	    env->idle != CPU_NOT_IDLE &&
-	    sgs->sum_h_nr_running &&
-	    sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu)) {
+	    env->idle != CPU_NOT_IDLE && sgs->sum_h_nr_running &&
+	    sched_asym(env, sds, sgs, group)) {
 		sgs->group_asym_packing = 1;
 	}
 
-	sgs->group_capacity = group->sgc->capacity;
-
-	sgs->group_weight = group->group_weight;
-
 	sgs->group_type = group_classify(env->sd->imbalance_pct, group, sgs);
 
 	/* Computing avg_load makes sense only when group is overloaded */
-- 
2.17.1