On Mon, Aug 19, 2013 at 9:00 AM, Peter Zijlstra <[email protected]> wrote:
> From: Joonsoo Kim <[email protected]>
>
> 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 <[email protected]>
> [peterz: expanded changelog]
> Signed-off-by: Peter Zijlstra <[email protected]>
> Link:
> http://lkml.kernel.org/r/[email protected]
> ---
> kernel/sched/fair.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5018,7 +5018,7 @@ static struct rq *find_busiest_queue(str
> struct sched_group *group)
> {
> struct rq *busiest = NULL, *rq;
> - unsigned long max_load = 0;
> + unsigned long busiest_load = 0, busiest_power = SCHED_POWER_SCALE;
Initializing this to SCHED_POWER_SCALE assigns a meaning that isn't
really there. How about just 1?
> int i;
>
> for_each_cpu(i, sched_group_cpus(group)) {
> @@ -5049,10 +5049,9 @@ static struct rq *find_busiest_queue(str
> * 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;
A comment wouldn't hurt here.
> + if (wl * busiest_power > busiest_load * power) {
> + busiest_load = wl;
> + busiest_power = power;
> busiest = rq;
> }
> }
>
>
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