sched: Allow for overlapping sched_domain spans

Allow for sched_domain spans that overlap by giving such domains their
own sched_group list instead of sharing the sched_groups amongst
each-other.

This is needed for machines with more than 16 nodes, because
sched_domain_node_span() will generate a node mask from the
16 nearest nodes without regard if these masks have any overlap.

Currently sched_domains have a sched_group that maps to their child
sched_domain span, and since there is no overlap we share the
sched_group between the sched_domains of the various CPUs. If however
there is overlap, we would need to link the sched_group list in
different ways for each cpu, and hence sharing isn't possible.

In order to solve this, allocate private sched_groups for each CPU's
sched_domain but have the sched_groups share a sched_group_power
structure such that we can uniquely track the power.

Reported-and-tested-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-08bxqw9wis3qti9u5inifh3y@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 132 insertions, 29 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2e5b3c8e2d3e..bde99d5358dc 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -844,6 +844,7 @@ enum cpu_idle_type {
 #define SD_SERIALIZE            0x0400  /* Only a single load balancing instance */
 #define SD_ASYM_PACKING         0x0800  /* Place busy groups earlier in the domain */
 #define SD_PREFER_SIBLING       0x1000  /* Prefer to place tasks in a sibling domain */
+#define SD_OVERLAP              0x2000  /* sched_domains of this level overlap */
 
 enum powersavings_balance_level {
         POWERSAVINGS_BALANCE_NONE = 0,  /* No power saving load balance */
@@ -894,6 +895,7 @@ static inline int sd_power_saving_flags(void)
 }
 
 struct sched_group_power {
+        atomic_t ref;
         /*
          * CPU power of this group, SCHED_LOAD_SCALE being max power for a
          * single CPU.
diff --git a/kernel/sched.c b/kernel/sched.c
index 36c10d25d4cd..921adf6f6fad 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6774,10 +6774,36 @@ static struct root_domain *alloc_rootdomain(void)
         return rd;
 }
 
+static void free_sched_groups(struct sched_group *sg, int free_sgp)
+{
+        struct sched_group *tmp, *first;
+
+        if (!sg)
+                return;
+
+        first = sg;
+        do {
+                tmp = sg->next;
+
+                if (free_sgp && atomic_dec_and_test(&sg->sgp->ref))
+                        kfree(sg->sgp);
+
+                kfree(sg);
+                sg = tmp;
+        } while (sg != first);
+}
+
 static void free_sched_domain(struct rcu_head *rcu)
 {
         struct sched_domain *sd = container_of(rcu, struct sched_domain, rcu);
-        if (atomic_dec_and_test(&sd->groups->ref)) {
+
+        /*
+         * If its an overlapping domain it has private groups, iterate and
+         * nuke them all.
+         */
+        if (sd->flags & SD_OVERLAP) {
+                free_sched_groups(sd->groups, 1);
+        } else if (atomic_dec_and_test(&sd->groups->ref)) {
                 kfree(sd->groups->sgp);
                 kfree(sd->groups);
         }
@@ -6967,15 +6993,73 @@ struct sched_domain_topology_level;
 typedef struct sched_domain *(*sched_domain_init_f)(struct sched_domain_topology_level *tl, int cpu);
 typedef const struct cpumask *(*sched_domain_mask_f)(int cpu);
 
+#define SDTL_OVERLAP    0x01
+
 struct sched_domain_topology_level {
         sched_domain_init_f init;
         sched_domain_mask_f mask;
+        int                 flags;
         struct sd_data      data;
 };
 
-/*
- * Assumes the sched_domain tree is fully constructed
- */
+static int
+build_overlap_sched_groups(struct sched_domain *sd, int cpu)
+{
+        struct sched_group *first = NULL, *last = NULL, *groups = NULL, *sg;
+        const struct cpumask *span = sched_domain_span(sd);
+        struct cpumask *covered = sched_domains_tmpmask;
+        struct sd_data *sdd = sd->private;
+        struct sched_domain *child;
+        int i;
+
+        cpumask_clear(covered);
+
+        for_each_cpu(i, span) {
+                struct cpumask *sg_span;
+
+                if (cpumask_test_cpu(i, covered))
+                        continue;
+
+                sg = kzalloc_node(sizeof(struct sched_group) + cpumask_size(),
+                                GFP_KERNEL, cpu_to_node(i));
+
+                if (!sg)
+                        goto fail;
+
+                sg_span = sched_group_cpus(sg);
+
+                child = *per_cpu_ptr(sdd->sd, i);
+                if (child->child) {
+                        child = child->child;
+                        cpumask_copy(sg_span, sched_domain_span(child));
+                } else
+                        cpumask_set_cpu(i, sg_span);
+
+                cpumask_or(covered, covered, sg_span);
+
+                sg->sgp = *per_cpu_ptr(sdd->sgp, cpumask_first(sg_span));
+                atomic_inc(&sg->sgp->ref);
+
+                if (cpumask_test_cpu(cpu, sg_span))
+                        groups = sg;
+
+                if (!first)
+                        first = sg;
+                if (last)
+                        last->next = sg;
+                last = sg;
+                last->next = first;
+        }
+        sd->groups = groups;
+
+        return 0;
+
+fail:
+        free_sched_groups(first, 0);
+
+        return -ENOMEM;
+}
+
 static int get_group(int cpu, struct sd_data *sdd, struct sched_group **sg)
 {
         struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu);
@@ -6987,23 +7071,21 @@ static int get_group(int cpu, struct sd_data *sdd, struct sched_group **sg)
         if (sg) {
                 *sg = *per_cpu_ptr(sdd->sg, cpu);
                 (*sg)->sgp = *per_cpu_ptr(sdd->sgp, cpu);
+                atomic_set(&(*sg)->sgp->ref, 1); /* for claim_allocations */
         }
 
         return cpu;
 }
 
 /*
- * build_sched_groups takes the cpumask we wish to span, and a pointer
- * to a function which identifies what group(along with sched group) a CPU
- * belongs to. The return value of group_fn must be a >= 0 and < nr_cpu_ids
- * (due to the fact that we keep track of groups covered with a struct cpumask).
- *
  * build_sched_groups will build a circular linked list of the groups
  * covered by the given span, and will set each group's ->cpumask correctly,
  * and ->cpu_power to 0.
+ *
+ * Assumes the sched_domain tree is fully constructed
  */
-static void
-build_sched_groups(struct sched_domain *sd)
+static int
+build_sched_groups(struct sched_domain *sd, int cpu)
 {
         struct sched_group *first = NULL, *last = NULL;
         struct sd_data *sdd = sd->private;
@@ -7011,6 +7093,12 @@ build_sched_groups(struct sched_domain *sd)
         struct cpumask *covered;
         int i;
 
+        get_group(cpu, sdd, &sd->groups);
+        atomic_inc(&sd->groups->ref);
+
+        if (cpu != cpumask_first(sched_domain_span(sd)))
+                return 0;
+
         lockdep_assert_held(&sched_domains_mutex);
         covered = sched_domains_tmpmask;
 
@@ -7042,6 +7130,8 @@ build_sched_groups(struct sched_domain *sd)
                 last = sg;
         }
         last->next = first;
+
+        return 0;
 }
 
 /*
@@ -7056,12 +7146,17 @@ build_sched_groups(struct sched_domain *sd)
  */
 static void init_sched_groups_power(int cpu, struct sched_domain *sd)
 {
-        WARN_ON(!sd || !sd->groups);
+        struct sched_group *sg = sd->groups;
 
-        if (cpu != group_first_cpu(sd->groups))
-                return;
+        WARN_ON(!sd || !sg);
+
+        do {
+                sg->group_weight = cpumask_weight(sched_group_cpus(sg));
+                sg = sg->next;
+        } while (sg != sd->groups);
 
-        sd->groups->group_weight = cpumask_weight(sched_group_cpus(sd->groups));
+        if (cpu != group_first_cpu(sg))
+                return;
 
         update_group_power(sd, cpu);
 }
@@ -7182,16 +7277,15 @@ static enum s_alloc __visit_domain_allocation_hell(struct s_data *d,
 static void claim_allocations(int cpu, struct sched_domain *sd)
 {
         struct sd_data *sdd = sd->private;
-        struct sched_group *sg = sd->groups;
 
         WARN_ON_ONCE(*per_cpu_ptr(sdd->sd, cpu) != sd);
         *per_cpu_ptr(sdd->sd, cpu) = NULL;
 
-        if (cpu == cpumask_first(sched_group_cpus(sg))) {
-                WARN_ON_ONCE(*per_cpu_ptr(sdd->sg, cpu) != sg);
+        if (atomic_read(&(*per_cpu_ptr(sdd->sg, cpu))->ref))
                 *per_cpu_ptr(sdd->sg, cpu) = NULL;
+
+        if (atomic_read(&(*per_cpu_ptr(sdd->sgp, cpu))->ref))
                 *per_cpu_ptr(sdd->sgp, cpu) = NULL;
-        }
 }
 
 #ifdef CONFIG_SCHED_SMT
@@ -7216,7 +7310,7 @@ static struct sched_domain_topology_level default_topology[] = {
 #endif
         { sd_init_CPU, cpu_cpu_mask, },
 #ifdef CONFIG_NUMA
-        { sd_init_NODE, cpu_node_mask, },
+        { sd_init_NODE, cpu_node_mask, SDTL_OVERLAP, },
         { sd_init_ALLNODES, cpu_allnodes_mask, },
 #endif
         { NULL, },
@@ -7284,7 +7378,9 @@ static void __sdt_free(const struct cpumask *cpu_map)
                 struct sd_data *sdd = &tl->data;
 
                 for_each_cpu(j, cpu_map) {
-                        kfree(*per_cpu_ptr(sdd->sd, j));
+                        struct sched_domain *sd = *per_cpu_ptr(sdd->sd, j);
+                        if (sd && (sd->flags & SD_OVERLAP))
+                                free_sched_groups(sd->groups, 0);
                         kfree(*per_cpu_ptr(sdd->sg, j));
                         kfree(*per_cpu_ptr(sdd->sgp, j));
                 }
@@ -7336,8 +7432,11 @@ static int build_sched_domains(const struct cpumask *cpu_map,
                 struct sched_domain_topology_level *tl;
 
                 sd = NULL;
-                for (tl = sched_domain_topology; tl->init; tl++)
+                for (tl = sched_domain_topology; tl->init; tl++) {
                         sd = build_sched_domain(tl, &d, cpu_map, attr, sd, i);
+                        if (tl->flags & SDTL_OVERLAP || sched_feat(FORCE_SD_OVERLAP))
+                                sd->flags |= SD_OVERLAP;
+                }
 
                 while (sd->child)
                         sd = sd->child;
@@ -7349,13 +7448,13 @@ static int build_sched_domains(const struct cpumask *cpu_map,
         for_each_cpu(i, cpu_map) {
                 for (sd = *per_cpu_ptr(d.sd, i); sd; sd = sd->parent) {
                         sd->span_weight = cpumask_weight(sched_domain_span(sd));
-                        get_group(i, sd->private, &sd->groups);
-                        atomic_inc(&sd->groups->ref);
-
-                        if (i != cpumask_first(sched_domain_span(sd)))
-                                continue;
-
-                        build_sched_groups(sd);
+                        if (sd->flags & SD_OVERLAP) {
+                                if (build_overlap_sched_groups(sd, i))
+                                        goto error;
+                        } else {
+                                if (build_sched_groups(sd, i))
+                                        goto error;
+                        }
                 }
         }
 
diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index be40f7371ee1..1e7066d76c26 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -70,3 +70,5 @@ SCHED_FEAT(NONIRQ_POWER, 1)
  * using the scheduler IPI. Reduces rq->lock contention/bounces.
  */
 SCHED_FEAT(TTWU_QUEUE, 1)
+
+SCHED_FEAT(FORCE_SD_OVERLAP, 0)