Re: [PATCH v2 1/5] sched/fair: Move select_task_rq_fair slow-path into its own function

[Vincent Guittot]

On 25 August 2017 at 12:16, Brendan Jackman <brendan.jackman@xxxxxxx> wrote:
> In preparation for changes that would otherwise require adding a new
> level of indentation to the while(sd) loop, create a new function
> find_idlest_cpu which contains this loop, and rename the existing
> find_idlest_cpu to find_idlest_group_cpu.
>
> Code inside the while(sd) loop is unchanged. @new_cpu is added as a
> variable in the new function, with the same initial value as the
> @new_cpu in select_task_rq_fair.
>
> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Brendan Jackman <brendan.jackman@xxxxxxx>
> Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> Cc: Josef Bacik <josef@xxxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Morten Rasmussen <morten.rasmussen@xxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

>
> squash! sched/fair: Move select_task_rq_fair slow-path into its own function
> ---
>  kernel/sched/fair.c | 83 +++++++++++++++++++++++++++++++----------------------
>  1 file changed, 48 insertions(+), 35 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c95880e216f6..f6e277c65235 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5509,10 +5509,10 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
>  }
>
>  /*
> - * find_idlest_cpu - find the idlest cpu among the cpus in group.
> + * find_idlest_group_cpu - find the idlest cpu among the cpus in group.
>   */
>  static int
> -find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
> +find_idlest_group_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
>  {
>         unsigned long load, min_load = ULONG_MAX;
>         unsigned int min_exit_latency = UINT_MAX;
> @@ -5561,6 +5561,50 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
>         return shallowest_idle_cpu != -1 ? shallowest_idle_cpu : least_loaded_cpu;
>  }
>
> +static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p,
> +                                 int cpu, int prev_cpu, int sd_flag)
> +{
> +       int new_cpu = prev_cpu;
> +
> +       while (sd) {
> +               struct sched_group *group;
> +               struct sched_domain *tmp;
> +               int weight;
> +
> +               if (!(sd->flags & sd_flag)) {
> +                       sd = sd->child;
> +                       continue;
> +               }
> +
> +               group = find_idlest_group(sd, p, cpu, sd_flag);
> +               if (!group) {
> +                       sd = sd->child;
> +                       continue;
> +               }
> +
> +               new_cpu = find_idlest_group_cpu(group, p, cpu);
> +               if (new_cpu == -1 || new_cpu == cpu) {
> +                       /* Now try balancing at a lower domain level of cpu */
> +                       sd = sd->child;
> +                       continue;
> +               }
> +
> +               /* Now try balancing at a lower domain level of new_cpu */
> +               cpu = new_cpu;
> +               weight = sd->span_weight;
> +               sd = NULL;
> +               for_each_domain(cpu, tmp) {
> +                       if (weight <= tmp->span_weight)
> +                               break;
> +                       if (tmp->flags & sd_flag)
> +                               sd = tmp;
> +               }
> +               /* while loop will break here if sd == NULL */
> +       }
> +
> +       return new_cpu;
> +}
> +
>  #ifdef CONFIG_SCHED_SMT
>
>  static inline void set_idle_cores(int cpu, int val)
> @@ -5918,39 +5962,8 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
>                 if (sd_flag & SD_BALANCE_WAKE) /* XXX always ? */
>                         new_cpu = select_idle_sibling(p, prev_cpu, new_cpu);
>
> -       } else while (sd) {
> -               struct sched_group *group;
> -               int weight;
> -
> -               if (!(sd->flags & sd_flag)) {
> -                       sd = sd->child;
> -                       continue;
> -               }
> -
> -               group = find_idlest_group(sd, p, cpu, sd_flag);
> -               if (!group) {
> -                       sd = sd->child;
> -                       continue;
> -               }
> -
> -               new_cpu = find_idlest_cpu(group, p, cpu);
> -               if (new_cpu == -1 || new_cpu == cpu) {
> -                       /* Now try balancing at a lower domain level of cpu */
> -                       sd = sd->child;
> -                       continue;
> -               }
> -
> -               /* Now try balancing at a lower domain level of new_cpu */
> -               cpu = new_cpu;
> -               weight = sd->span_weight;
> -               sd = NULL;
> -               for_each_domain(cpu, tmp) {
> -                       if (weight <= tmp->span_weight)
> -                               break;
> -                       if (tmp->flags & sd_flag)
> -                               sd = tmp;
> -               }
> -               /* while loop will break here if sd == NULL */
> +       } else {
> +               new_cpu = find_idlest_cpu(sd, p, cpu, prev_cpu, sd_flag);
>         }
>         rcu_read_unlock();
>
> --
> 2.14.1
>