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    Subject[tip:sched/core] sched: Remove one division operation in find_busiest_queue()
    Commit-ID:  95a79b805b935f4a7b685aa8a117d916c638323e
    Gitweb: http://git.kernel.org/tip/95a79b805b935f4a7b685aa8a117d916c638323e
    Author: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    AuthorDate: Tue, 6 Aug 2013 17:36:41 +0900
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Mon, 2 Sep 2013 08:26:59 +0200

    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 <iamjoonsoo.kim@lge.com>
    [ Expanded the changelog. ]
    Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    Link: http://lkml.kernel.org/r/1375778203-31343-2-git-send-email-iamjoonsoo.kim@lge.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    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 f918635..8aa217f 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;
    }
    }

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