From 95a79b805b935f4a7b685aa8a117d916c638323e Mon Sep 17 00:00:00 2001 From: Joonsoo Kim Date: Tue, 6 Aug 2013 17:36:41 +0900 Subject: [PATCH] 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: Joonsoo Kim [ Expanded the changelog. ] Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/1375778203-31343-2-git-send-email-iamjoonsoo.kim@lge.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index f918635efe09..8aa217f62a9e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -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. + * + * 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. */ - wl = (wl * SCHED_POWER_SCALE) / power; - - if (wl > max_load) { - max_load = wl; + if (wl * busiest_power > busiest_load * power) { + busiest_load = wl; + busiest_power = power; busiest = rq; } } -- 2.20.1