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[PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology

Started byByungchul Park <byungchul.park@lge.com>
First post2017-08-07 06:00 +0200
Last post2017-08-07 06:00 +0200
Articles 4 — 1 participant

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  [PATCH v6 0/2]  Make find_later_rq() choose a closer cpu in topology Byungchul Park <byungchul.park@lge.com> - 2017-08-07 06:00 +0200
    [PATCH v6 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq() Byungchul Park <byungchul.park@lge.com> - 2017-08-07 06:00 +0200
      Re: [PATCH v6 2/2] sched/rt: Add support for SD_PREFER_SIBLING on  find_lowest_rq() Byungchul Park <byungchul.park@lge.com> - 2017-08-10 14:20 +0200
    [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() Byungchul Park <byungchul.park@lge.com> - 2017-08-07 06:00 +0200

#1705078 — [PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology

FromByungchul Park <byungchul.park@lge.com>
Date2017-08-07 06:00 +0200
Subject[PATCH v6 0/2] Make find_later_rq() choose a closer cpu in topology
Message-ID<ubHmV-2YE-7@gated-at.bofh.it>
When cpudl_find() returns any among free_cpus, the cpu might not be
closer than others, considering sched domain. For example:

   this_cpu: 15
   free_cpus: 0, 1,..., 14 (== later_mask)
   best_cpu: 0

   topology:

   0 --+
       +--+
   1 --+  |
          +-- ... --+
   2 --+  |         |
       +--+         |
   3 --+            |

   ...             ...

   12 --+           |
        +--+        |
   13 --+  |        |
           +-- ... -+
   14 --+  |
        +--+
   15 --+

In this case, it would be best to select 14 since it's a free cpu and
closest to 15(this_cpu). However, currently the code select 0(best_cpu)
even though that's just any among free_cpus. Fix it.

Change from v5
   -. exclude two patches already picked up by peterz
      (sched/deadline: Make find_later_rq() choose a closer cpu in topology)
      (sched/deadline: Change return value of cpudl_find())
   -. apply what peterz fixed for 'prefer sibling', into deadline and rt

Change from v4
   -. remove a patch that might cause huge lock contention
      (by spin lock(&cpudl.lock) in a hot path of scheduler)

Change from v3
   -. rename closest_cpu to best_cpu so that it align with rt
   -. protect referring cpudl.elements with cpudl.lock
   -. change return value of cpudl_find() to bool

Change from v2
   -. add support for SD_PREFER_SIBLING

Change from v1
   -. clean up the patch

Byungchul Park (2):
  sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
  sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()

 kernel/sched/deadline.c | 46 +++++++++++++++++++++++++++++++++++++++++++---
 kernel/sched/rt.c       | 47 ++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 87 insertions(+), 6 deletions(-)

-- 
1.9.1

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#1705080 — [PATCH v6 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()

FromByungchul Park <byungchul.park@lge.com>
Date2017-08-07 06:00 +0200
Subject[PATCH v6 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()
Message-ID<ubHmW-2YE-21@gated-at.bofh.it>
In reply to#1705078
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/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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#1708539 — Re: [PATCH v6 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()

FromByungchul Park <byungchul.park@lge.com>
Date2017-08-10 14:20 +0200
SubjectRe: [PATCH v6 2/2] sched/rt: Add support for SD_PREFER_SIBLING on find_lowest_rq()
Message-ID<ucUBv-5tj-81@gated-at.bofh.it>
In reply to#1705080
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.park@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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#1705081 — [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()

FromByungchul Park <byungchul.park@lge.com>
Date2017-08-07 06:00 +0200
Subject[PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq()
Message-ID<ubHmW-2YE-17@gated-at.bofh.it>
In reply to#1705078
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 | 46 +++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 43 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 0223694..2fd1591 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 +1407,17 @@ 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 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;
 			}
@@ -1393,6 +1426,13 @@ 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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