Re: [PATCH 00/14] sched/topology fixes

[Peter Zijlstra]

On Fri, Apr 28, 2017 at 08:30:05PM -0300, Lauro Venancio wrote:
> On 04/28/2017 10:53 AM, Peter Zijlstra wrote:
> > Also, the following occurred to me:
> >
> >   sg_span & sg_mask == sg_mask
> >
> > Therefore, we don't need to do the whole "sg_span &" business.
> >
> > Hmm?

> Agreed. Maybe we have to rename "mask" to something else. Maybe
> "group_reached_by_cpus" or "group_installed_on_cpus".

I went with group_balance_mask() to match the existing
group_balance_cpu().

And now the temptation is very great to also fix up the
sched_group_cpus() vs sched_domain_span() thing...

---
Subject: sched/topology: Rename sched_group_mask()
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Mon May 1 10:47:02 CEST 2017

Since sched_group_mask() is now an independent cpumask (it no longer
masks sched_group_cpus()), rename the thing.

Suggested-by: Lauro Ramos Venancio <lvenanci@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/sched/fair.c     |    4 +---
 kernel/sched/sched.h    |    7 +++----
 kernel/sched/topology.c |   31 ++++++++++++++-----------------
 3 files changed, 18 insertions(+), 24 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7996,7 +7996,6 @@ static int active_load_balance_cpu_stop(
 static int should_we_balance(struct lb_env *env)
 {
 	struct sched_group *sg = env->sd->groups;
-	struct cpumask *sg_mask;
 	int cpu, balance_cpu = -1;
 
 	/*
@@ -8006,9 +8005,8 @@ static int should_we_balance(struct lb_e
 	if (env->idle == CPU_NEWLY_IDLE)
 		return 1;
 
-	sg_mask = sched_group_mask(sg);
 	/* Try to find first idle cpu */
-	for_each_cpu_and(cpu, sg_mask, env->cpus) {
+	for_each_cpu_and(cpu, group_balance_mask(sg), env->cpus) {
 		if (!idle_cpu(cpu))
 			continue;
 
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1027,7 +1027,7 @@ struct sched_group_capacity {
 	int id;
 #endif
 
-	unsigned long cpumask[0]; /* iteration mask */
+	unsigned long cpumask[0]; /* balance mask */
 };
 
 struct sched_group {
@@ -1054,10 +1054,9 @@ static inline struct cpumask *sched_grou
 }
 
 /*
- * cpumask masking which cpus in the group are allowed to iterate up the domain
- * tree.
+ * See build_balance_mask().
  */
-static inline struct cpumask *sched_group_mask(struct sched_group *sg)
+static inline struct cpumask *group_balance_mask(struct sched_group *sg)
 {
 	return to_cpumask(sg->sgc->cpumask);
 }
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -86,9 +86,9 @@ static int sched_domain_debug_one(struct
 				cpumask_pr_args(sched_group_cpus(group)));
 
 		if ((sd->flags & SD_OVERLAP) &&
-		    !cpumask_equal(sched_group_mask(group), sched_group_cpus(group))) {
+		    !cpumask_equal(group_balance_mask(group), sched_group_cpus(group))) {
 			printk(KERN_CONT " mask=%*pbl",
-				cpumask_pr_args(sched_group_mask(group)));
+				cpumask_pr_args(group_balance_mask(group)));
 		}
 
 		if (group->sgc->capacity != SCHED_CAPACITY_SCALE)
@@ -497,16 +497,16 @@ enum s_alloc {
 
 /*
  * Return the canonical balance CPU for this group, this is the first CPU
- * of this group that's also in the iteration mask.
+ * of this group that's also in the balance mask.
  *
- * The iteration mask are all those CPUs that could actually end up at this
- * group. See build_group_mask().
+ * The balance mask are all those CPUs that could actually end up at this
+ * group. See build_balance_mask().
  *
  * Also see should_we_balance().
  */
 int group_balance_cpu(struct sched_group *sg)
 {
-	return cpumask_first(sched_group_mask(sg));
+	return cpumask_first(group_balance_mask(sg));
 }
 
 
@@ -563,7 +563,7 @@ int group_balance_cpu(struct sched_group
  * groups include the CPUs of Node-0, while those CPUs would not in fact ever
  * end up at those groups (they would end up in group: 0-1,3).
  *
- * To correct this we have to introduce the group iteration mask. This mask
+ * To correct this we have to introduce the group balance mask. This mask
  * will contain those CPUs in the group that can reach this group given the
  * (child) domain tree.
  *
@@ -607,11 +607,8 @@ int group_balance_cpu(struct sched_group
 
 
 /*
- * Build an iteration mask that can exclude certain CPUs from the upwards
- * domain traversal.
- *
- * Only CPUs that can arrive at this group should be considered to continue
- * balancing.
+ * Build the balance mask; it contains only those CPUs that can arrive at this
+ * group and should be considered to continue balancing.
  *
  * We do this during the group creation pass, therefore the group information
  * isn't complete yet, however since each group represents a (child) domain we
@@ -619,7 +616,7 @@ int group_balance_cpu(struct sched_group
  * complete).
  */
 static void
-build_group_mask(struct sched_domain *sd, struct sched_group *sg, struct cpumask *mask)
+build_balance_mask(struct sched_domain *sd, struct sched_group *sg, struct cpumask *mask)
 {
 	const struct cpumask *sg_span = sched_group_cpus(sg);
 	struct sd_data *sdd = sd->private;
@@ -684,14 +681,14 @@ static void init_overlap_sched_group(str
 	struct cpumask *sg_span;
 	int cpu;
 
-	build_group_mask(sd, sg, mask);
+	build_balance_mask(sd, sg, mask);
 	cpu = cpumask_first_and(sched_group_cpus(sg), mask);
 
 	sg->sgc = *per_cpu_ptr(sdd->sgc, cpu);
 	if (atomic_inc_return(&sg->sgc->ref) == 1)
-		cpumask_copy(sched_group_mask(sg), mask);
+		cpumask_copy(group_balance_mask(sg), mask);
 	else
-		WARN_ON_ONCE(!cpumask_equal(sched_group_mask(sg), mask));
+		WARN_ON_ONCE(!cpumask_equal(group_balance_mask(sg), mask));
 
 	/*
 	 * Initialize sgc->capacity such that even if we mess up the
@@ -888,7 +885,7 @@ build_sched_groups(struct sched_domain *
 			continue;
 
 		group = get_group(i, sdd, &sg);
-		cpumask_copy(sched_group_mask(sg), sched_group_cpus(sg));
+		cpumask_copy(group_balance_mask(sg), sched_group_cpus(sg));
 
 		for_each_cpu(j, span) {
 			if (get_group(j, sdd, NULL) != group)