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

[Byungchul Park]

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  
> 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 
> > ---
> >  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.

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

[Byungchul Park]

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  
> 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 
> > ---
> >  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.

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

[Joel Fernandes (Google)]

Hi Byungchul,

On Thu, Aug 17, 2017 at 11:05 PM, 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.
>
> Signed-off-by: Byungchul Park 
> ---
>  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

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

[Joel Fernandes (Google)]

Hi Byungchul,

On Thu, Aug 17, 2017 at 11:05 PM, 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.
>
> Signed-off-by: Byungchul Park 
> ---
>  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

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

[Byungchul Park]

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 
---
 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

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

[Byungchul Park]

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 
---
 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