Hi,
LGTM. Tiny inline comment but TBH might not be worth it.
FWIW: Reviewed-by: Valentin Schneider <valentin.schnei...@arm.com>
On 26/04/18 11:30, Viresh Kumar wrote:
> Rearrange select_task_rq_fair() a bit to avoid executing some
> conditional statements in few specific code-paths. That gets rid of the
> goto as well.
>
> This shouldn't result in any functional changes.
>
> Signed-off-by: Viresh Kumar <viresh.ku...@linaro.org>
> Tested-by: Rohit Jain <rohit.k.j...@oracle.com>
>
> ---
> V1->V2:
> - Optimize a bit more and get rid of affine_sd variable (Valentin)
> - Add unlikely while checking for non-NULL sd and add fast/slow path
> comments (Joel)
> - Add tested-by from Rohit.
>
> kernel/sched/fair.c | 37 ++++++++++++++++---------------------
> 1 file changed, 16 insertions(+), 21 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 54dc31e7ab9b..84fc74ddbd4b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6613,7 +6613,7 @@ static int wake_cap(struct task_struct *p, int cpu, int
> prev_cpu)
> static int
> select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int
> wake_flags)
> {
> - struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
> + struct sched_domain *tmp, *sd = NULL;
> int cpu = smp_processor_id();
> int new_cpu = prev_cpu;
> int want_affine = 0;
> @@ -6636,7 +6636,10 @@ select_task_rq_fair(struct task_struct *p, int
> prev_cpu, int sd_flag, int wake_f
> */
> if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
> cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
> - affine_sd = tmp;
> + if (cpu != prev_cpu)
> + new_cpu = wake_affine(tmp, p, cpu, prev_cpu,
> sync);
This cpu != prev_cpu check could be folded into wake_affine() to make this
look a little neater, but we might want to keep things as is to avoid a
function call (it's only ever called once so it might get inlined, but AFAIK
that's not guaranteed).
> +
> + sd = NULL; /* Prefer wake_affine over balance flags */
> break;
> }
>
> @@ -6646,33 +6649,25 @@ select_task_rq_fair(struct task_struct *p, int
> prev_cpu, int sd_flag, int wake_f
> break;
> }
>
> - if (affine_sd) {
> - sd = NULL; /* Prefer wake_affine over balance flags */
> - if (cpu == prev_cpu)
> - goto pick_cpu;
> -
> - new_cpu = wake_affine(affine_sd, p, cpu, prev_cpu, sync);
> - }
> + if (unlikely(sd)) {
> + /* Slow path */
>
> - if (sd && !(sd_flag & SD_BALANCE_FORK)) {
> /*
> * We're going to need the task's util for capacity_spare_wake
> * in find_idlest_group. Sync it up to prev_cpu's
> * last_update_time.
> */
> - sync_entity_load_avg(&p->se);
> - }
> -
> - if (!sd) {
> -pick_cpu:
> - if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */
> - new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
> + if (!(sd_flag & SD_BALANCE_FORK))
> + sync_entity_load_avg(&p->se);
>
> - if (want_affine)
> - current->recent_used_cpu = cpu;
> - }
> - } else {
> new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag);
> + } else if (sd_flag & SD_BALANCE_WAKE) { /* XXX always ? */
> + /* Fast path */
> +
> + new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
> +
> + if (want_affine)
> + current->recent_used_cpu = cpu;
> }
> rcu_read_unlock();
>
>
