sched: add preference for prev and sibling CPU in HMP task placement

At present HMP task placement algorithm places wake-up task on any lowest
power cost CPU in the system even if the task's previous CPU is also one
of the lowest power cost CPU.  Placing task on the previous CPU can reduce
cache bouncing.

Add a bias towards the task's previous CPU and CPU in the same cache domain
with previous CPU.

Change-Id: Ieab3840432e277048058da76764b3a3f16e20c56
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>

1 files changed, 22 insertions, 8 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5923011cf92c..fc0ff96a1fd8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3182,9 +3182,9 @@ static int select_best_cpu(struct task_struct *p, int target, int reason,
 			   int sync)
 {
 	int i, best_cpu = -1, best_idle_cpu = -1, best_capacity_cpu = -1;
-	int prev_cpu = task_cpu(p);
-	int cpu_cost, min_cost = INT_MAX;
-	u64 tload, cpu_load;
+	int prev_cpu = task_cpu(p), best_sibling_cpu = -1;
+	int cpu_cost, min_cost = INT_MAX, best_sibling_cpu_cost = INT_MAX;
+	u64 tload, cpu_load, best_sibling_cpu_load = ULLONG_MAX;
 	u64 min_load = ULLONG_MAX;
 	s64 spare_capacity, highest_spare_capacity = 0;
 	int boost = sched_boost();
@@ -3238,21 +3238,32 @@ static int select_best_cpu(struct task_struct *p, int target, int reason,
 
 		cpu_cost = power_cost(tload + cpu_load, i);
 
+		if (cpu_cost > min_cost)
+			continue;
+
 		/*
 		 * If the task fits in a CPU in a lower power band, that
 		 * overrides all other considerations.
 		 */
 		if (power_delta_exceeded(cpu_cost, min_cost)) {
-			if (cpu_cost > min_cost)
-				continue;
-
 			min_cost = cpu_cost;
 			min_load = ULLONG_MAX;
 			best_cpu = -1;
 		}
 
-		if (cpu_cost < min_cost ||
-		    (cpu_cost == min_cost && cpu_load < min_load)) {
+		if (i != prev_cpu && cpus_share_cache(prev_cpu, i)) {
+			if (best_sibling_cpu_cost > cpu_cost ||
+			    (best_sibling_cpu_cost == cpu_cost &&
+			     best_sibling_cpu_load > cpu_load)) {
+				best_sibling_cpu_cost = cpu_cost;
+				best_sibling_cpu_load = cpu_load;
+				best_sibling_cpu = i;
+			}
+		}
+
+		if ((cpu_cost < min_cost) ||
+		    ((best_cpu != prev_cpu && min_load > cpu_load) ||
+		     i == prev_cpu)) {
 			if (need_idle) {
 				if (idle_cpu(i)) {
 					min_cost = cpu_cost;
@@ -3274,6 +3285,9 @@ static int select_best_cpu(struct task_struct *p, int target, int reason,
 			best_cpu = prev_cpu;
 		else
 			best_cpu = best_capacity_cpu;
+	} else {
+		if (best_cpu != prev_cpu && min_cost == best_sibling_cpu_cost)
+			best_cpu = best_sibling_cpu;
 	}
 
 	trace_sched_task_load(p, boost, reason, sync, need_idle);