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Commit 783ec9cf authored by Joonwoo Park's avatar Joonwoo Park
Browse files

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: default avatarJoonwoo Park <joonwoop@codeaurora.org>
parent 630fdcc6

kernel/sched/fair.c

+22 −8
Original line number Diff line number Diff line
@@ -2949,9 +2949,9 @@ 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();
@@ -3005,21 +3005,32 @@ 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;
@@ -3041,6 +3052,9 @@ 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);