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
> ---
> 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
