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Commit 352e0961 authored by Valentin Schneider's avatar Valentin Schneider Committed by Andres Oportus
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ANDROID: sched/fair: discount task contribution to find CPU with lowest utilization 



In some cases, the new_util of a task can be the same on several
CPUs. This causes an issue because the target_util is only updated
if the current new_util is strictly smaller than target_util.

To fix that, the cpu_util_wake() return value is used alongside the
new_util value. If two CPUs compute the same new_util value,
we'll now also look at their cpu_util_wake() return value. In this
case, the CPU that last ran the task will be chosen in priority.

Change-Id: Ia1ea2c4b3ec39621372c2f748862317d5b497723
Signed-off-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Signed-off-by: default avatarQuentin Perret <quentin.perret@arm.com>
parent db00ec15

kernel/sched/fair.c

+13 −4
Original line number Diff line number Diff line
@@ -6560,7 +6560,8 @@ static inline int find_best_target(struct task_struct *p, bool boosted, bool pre 
		int i;



		for_each_cpu_and(i, tsk_cpus_allowed(p), sched_group_cpus(sg)) {

			unsigned long cur_capacity, new_util;

			unsigned long cur_capacity, new_util, wake_util;

			unsigned long min_wake_util = ULONG_MAX;



			if (!cpu_online(i))

				continue;
@@ -6570,7 +6571,8 @@ static inline int find_best_target(struct task_struct *p, bool boosted, bool pre 
			 * so prev_cpu will receive a negative bias due to the double

			 * accounting. However, the blocked utilization may be zero.

			 */

			new_util = cpu_util_wake(i, p) + task_util(p);

			wake_util = cpu_util_wake(i, p);

			new_util = wake_util + task_util(p);



			/*

			 * Ensure minimum capacity to grant the required boost.
@@ -6604,8 +6606,15 @@ static inline int find_best_target(struct task_struct *p, bool boosted, bool pre 
					 * Find a target cpu with the lowest/highest

					 * utilization if prefer_idle/!prefer_idle.

					 */

					if ((prefer_idle && target_util > new_util) ||

					    (!prefer_idle && target_util < new_util)) {

					if (prefer_idle) {

						/* Favor the CPU that last ran the task */

						if (new_util > target_util ||

						    wake_util > min_wake_util)

							continue;

						min_wake_util = wake_util;

						target_util = new_util;

						target_cpu = i;

					} else if (target_util < new_util) {

						target_util = new_util;

						target_cpu = i;

					}