[PATCH 3/4] sched/fair: Let lower-priority CPUs do active balancing

[Ricardo Neri]

When more than one SMT siblings of a physical core are busy, an idle CPU
of lower priority can help.

Indicate that the low priority CPU can do active balancing from the high-
priority CPU only if they belong to separate cores.

Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Tim C. Chen <tim.c.chen@xxxxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Reviewed-by: Len Brown <len.brown@xxxxxxxxx>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
 kernel/sched/fair.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 810645eb58ed..9b608b31080f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9759,9 +9759,14 @@ asym_active_balance(struct lb_env *env)
 	 * ASYM_PACKING needs to force migrate tasks from busy but
 	 * lower priority CPUs in order to pack all tasks in the
 	 * highest priority CPUs.
+	 *
+	 * If the busy CPU has higher priority but is an SMT sibling
+	 * in which other SMT siblings are also busy, a lower-priority
+	 * CPU in a separate core can help.
 	 */
 	return env->idle != CPU_NOT_IDLE && (env->sd->flags & SD_ASYM_PACKING) &&
-	       sched_asym_prefer(env->dst_cpu, env->src_cpu);
+	       (sched_asym_prefer(env->dst_cpu, env->src_cpu) ||
+		!(env->sd->flags & SD_SHARE_CPUCAPACITY));
 }
 
 static inline bool
-- 
2.25.1