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[PATCH v7 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()

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  [PATCH v7 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Byungchul Park <byungchul.park@lge.com> - 2017-08-18 08:10 +0200
    Re: [PATCH v7 1/2] sched/deadline: Add support for SD_PREFER_SIBLING  on find_later_rq() "Joel Fernandes (Google)" <joel.opensrc@gmail.com> - 2017-08-18 09:30 +0200
      Re: [PATCH v7 1/2] sched/deadline: Add support for SD_PREFER_SIBLING  on find_later_rq() Byungchul Park <byungchul.park@lge.com> - 2017-08-18 10:00 +0200

#1714592 — [PATCH v7 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()

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.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
---
 kernel/sched/deadline.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 52 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 0223694..8f69a37 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1319,12 +1319,35 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
 
 static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
 
+/*
+ * 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_later_rq(struct task_struct *task)
 {
-	struct sched_domain *sd;
+	struct sched_domain *sd, *prefer = NULL;
 	struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl);
 	int this_cpu = smp_processor_id();
 	int cpu = task_cpu(task);
+	int fallback_cpu = -1;
 
 	/* Make sure the mask is initialized first */
 	if (unlikely(!later_mask))
@@ -1376,8 +1399,7 @@ static int find_later_rq(struct task_struct *task)
 				return this_cpu;
 			}
 
-			best_cpu = cpumask_first_and(later_mask,
-							sched_domain_span(sd));
+			best_cpu = find_cpu(later_mask, sd, prefer);
 			/*
 			 * Last chance: if a cpu being in both later_mask
 			 * and current sd span is valid, that becomes our
@@ -1385,6 +1407,26 @@ static int find_later_rq(struct task_struct *task)
 			 * already under consideration through later_mask.
 			 */
 			if (best_cpu < nr_cpu_ids) {
+				/*
+				 * If current domain is SD_PREFER_SIBLING
+				 * flaged, we have to try to check other
+				 * siblings first.
+				 */
+				if (sd->flags & SD_PREFER_SIBLING) {
+					prefer = sd;
+
+					/*
+					 * fallback_cpu should be one
+					 * in the closest domain among
+					 * SD_PREFER_SIBLING domains,
+					 * in case that more than one
+					 * SD_PREFER_SIBLING domains
+					 * exist in the hierachy.
+					 */
+					if (fallback_cpu == -1)
+						fallback_cpu = best_cpu;
+					continue;
+				}
 				rcu_read_unlock();
 				return best_cpu;
 			}
@@ -1393,6 +1435,13 @@ static int find_later_rq(struct task_struct *task)
 	rcu_read_unlock();
 
 	/*
+	 * If fallback_cpu is valid, all our guesses failed *except* for
+	 * SD_PREFER_SIBLING domain. Now, we can return the fallback cpu.
+	 */
+	if (fallback_cpu != -1)
+		return fallback_cpu;
+
+	/*
 	 * At this point, all our guesses failed, we just return
 	 * 'something', and let the caller sort the things out.
 	 */
-- 
1.9.1

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#1714631 — Re: [PATCH v7 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()

Hi Byungchul,

On Thu, Aug 17, 2017 at 11:05 PM, Byungchul Park <byungchul.park@lge.com> 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.
>
> Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> ---
>  kernel/sched/deadline.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 52 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 0223694..8f69a37 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1319,12 +1319,35 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
>
>  static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
>
> +/*
> + * 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) {

This can be simplified to for_each_cpu(cpu, mask) ?


thanks,

-Joel

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#1714659 — Re: [PATCH v7 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()

On Fri, Aug 18, 2017 at 12:21:46AM -0700, Joel Fernandes (Google) wrote:
> Hi Byungchul,
> 
> On Thu, Aug 17, 2017 at 11:05 PM, Byungchul Park <byungchul.park@lge.com> 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.
> >
> > Signed-off-by: Byungchul Park <byungchul.park@lge.com>
> > ---
> >  kernel/sched/deadline.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++---
> >  1 file changed, 52 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > index 0223694..8f69a37 100644
> > --- a/kernel/sched/deadline.c
> > +++ b/kernel/sched/deadline.c
> > @@ -1319,12 +1319,35 @@ static struct task_struct *pick_earliest_pushable_dl_task(struct rq *rq, int cpu
> >
> >  static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);
> >
> > +/*
> > + * 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) {
> 
> This can be simplified to for_each_cpu(cpu, mask) ?

Indeed, exactly.

I will use that, thank you.

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