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Commit 95a79b80 authored by Joonsoo Kim's avatar Joonsoo Kim Committed by Ingo Molnar
Browse files

sched: Remove one division operation in find_busiest_queue() 



Remove one division operation in find_busiest_queue() by using
crosswise multiplication:

	wl_i / power_i > wl_j / power_j :=
	wl_i * power_j > wl_j * power_i

Signed-off-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
[ Expanded the changelog. ]
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1375778203-31343-2-git-send-email-iamjoonsoo.kim@lge.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent a4f61cc0

kernel/sched/fair.c

+9 −5
Original line number Diff line number Diff line
@@ -4968,7 +4968,7 @@ static struct rq *find_busiest_queue(struct lb_env *env, 
				     struct sched_group *group)

{

	struct rq *busiest = NULL, *rq;

	unsigned long max_load = 0;

	unsigned long busiest_load = 0, busiest_power = 1;

	int i;



	for_each_cpu(i, sched_group_cpus(group)) {
@@ -4998,11 +4998,15 @@ static struct rq *find_busiest_queue(struct lb_env *env, 
		 * the weighted_cpuload() scaled with the cpu power, so that

		 * the load can be moved away from the cpu that is potentially

		 * running at a lower capacity.

		 */

		wl = (wl * SCHED_POWER_SCALE) / power;



		if (wl > max_load) {

			max_load = wl;

		 *

		 * Thus we're looking for max(wl_i / power_i), crosswise

		 * multiplication to rid ourselves of the division works out

		 * to: wl_i * power_j > wl_j * power_i;  where j is our

		 * previous maximum.

		 */

		if (wl * busiest_power > busiest_load * power) {

			busiest_load = wl;

			busiest_power = power;

			busiest = rq;

		}

	}