On Mon, Aug 07, 2017 at 12:50:34PM +0900, Byungchul Park wrote:
> It would be better to avoid pushing tasks to other cpu within
> a SD_PREFER_SIBLING domain, instead, get more chances to check other
> siblings.

I applied your suggestion. Could you let me know your opinions about
this?

> 
> Signed-off-by: Byungchul Park <byungchul.p...@lge.com>
> ---
>  kernel/sched/rt.c | 47 ++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 44 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 979b734..50639e5 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1618,12 +1618,35 @@ static struct task_struct 
> *pick_highest_pushable_task(struct rq *rq, int cpu)
>  
>  static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask);
>  
> +/*
> + * Find the first cpu in: mask & sd & ~prefer
> + */
> +static int find_cpu(const struct cpumask *mask,
> +                 const struct sched_domain *sd,
> +                 const struct sched_domain *prefer)
> +{
> +     const struct cpumask *sds = sched_domain_span(sd);
> +     const struct cpumask *ps  = prefer ? sched_domain_span(prefer) : NULL;
> +     int cpu = -1;
> +
> +     while ((cpu = cpumask_next(cpu, mask)) < nr_cpu_ids) {
> +             if (!cpumask_test_cpu(cpu, sds))
> +                     continue;
> +             if (ps && cpumask_test_cpu(cpu, ps))
> +                     continue;
> +             break;
> +     }
> +
> +     return cpu;
> +}
> +
>  static int find_lowest_rq(struct task_struct *task)
>  {
> -     struct sched_domain *sd;
> +     struct sched_domain *sd, *prefer = NULL;
>       struct cpumask *lowest_mask = this_cpu_cpumask_var_ptr(local_cpu_mask);
>       int this_cpu = smp_processor_id();
>       int cpu      = task_cpu(task);
> +     int fallback_cpu = -1;
>  
>       /* Make sure the mask is initialized first */
>       if (unlikely(!lowest_mask))
> @@ -1668,9 +1691,20 @@ static int find_lowest_rq(struct task_struct *task)
>                               return this_cpu;
>                       }
>  
> -                     best_cpu = cpumask_first_and(lowest_mask,
> -                                                  sched_domain_span(sd));
> +                     best_cpu = find_cpu(lowest_mask, sd, prefer);
> +
>                       if (best_cpu < nr_cpu_ids) {
> +                             /*
> +                              * If current domain is SD_PREFER_SIBLING
> +                              * flaged, we have to get more chances to
> +                              * check other siblings.
> +                              */
> +                             if (sd->flags & SD_PREFER_SIBLING) {
> +                                     prefer = sd;
> +                                     if (fallback_cpu == -1)
> +                                             fallback_cpu = best_cpu;
> +                                     continue;
> +                             }
>                               rcu_read_unlock();
>                               return best_cpu;
>                       }
> @@ -1679,6 +1713,13 @@ static int find_lowest_rq(struct task_struct *task)
>       rcu_read_unlock();
>  
>       /*
> +      * If fallback_cpu is valid, all our quesses failed *except* for
> +      * SD_PREFER_SIBLING domain. Now, we can return the fallback cpu.
> +      */
> +     if (fallback_cpu != -1)
> +             return fallback_cpu;
> +
> +     /*
>        * And finally, if there were no matches within the domains
>        * just give the caller *something* to work with from the compatible
>        * locations.
> -- 
> 1.9.1

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