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Subject[PATCH v4 03/10] sched/topology: Provide cfs_overload_cpus bitmap
Date
From: Steve Sistare <steve.sistare@oracle.com>

Define and initialize a sparse bitmap of overloaded CPUs, per
last-level-cache scheduling domain, for use by the CFS scheduling class.
Save a pointer to cfs_overload_cpus in the rq for efficient access.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
include/linux/sched/topology.h | 1 +
kernel/sched/sched.h | 2 ++
kernel/sched/topology.c | 25 +++++++++++++++++++++++--
3 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index 6b99761..b173a77 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -72,6 +72,7 @@ struct sched_domain_shared {
atomic_t ref;
atomic_t nr_busy_cpus;
int has_idle_cores;
+ struct sparsemask *cfs_overload_cpus;
};

struct sched_domain {
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 618577f..eacf5db 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -81,6 +81,7 @@

struct rq;
struct cpuidle_state;
+struct sparsemask;

/* task_struct::on_rq states: */
#define TASK_ON_RQ_QUEUED 1
@@ -812,6 +813,7 @@ struct rq {
struct cfs_rq cfs;
struct rt_rq rt;
struct dl_rq dl;
+ struct sparsemask *cfs_overload_cpus;

#ifdef CONFIG_FAIR_GROUP_SCHED
/* list of leaf cfs_rq on this CPU: */
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 3e72ce0..89a78ce 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -3,6 +3,7 @@
* Scheduler topology setup/handling methods
*/
#include "sched.h"
+#include "sparsemask.h"

DEFINE_MUTEX(sched_domains_mutex);

@@ -410,7 +411,9 @@ static void destroy_sched_domains(struct sched_domain *sd)

static void update_top_cache_domain(int cpu)
{
+ struct sparsemask *cfs_overload_cpus = NULL;
struct sched_domain_shared *sds = NULL;
+ struct rq *rq = cpu_rq(cpu);
struct sched_domain *sd;
int id = cpu;
int size = 1;
@@ -420,8 +423,10 @@ static void update_top_cache_domain(int cpu)
id = cpumask_first(sched_domain_span(sd));
size = cpumask_weight(sched_domain_span(sd));
sds = sd->shared;
+ cfs_overload_cpus = sds->cfs_overload_cpus;
}

+ rcu_assign_pointer(rq->cfs_overload_cpus, cfs_overload_cpus);
rcu_assign_pointer(per_cpu(sd_llc, cpu), sd);
per_cpu(sd_llc_size, cpu) = size;
per_cpu(sd_llc_id, cpu) = id;
@@ -1621,7 +1626,22 @@ static void __sdt_free(const struct cpumask *cpu_map)

static int sd_llc_alloc(struct sched_domain *sd)
{
- /* Allocate sd->shared data here. Empty for now. */
+ struct sched_domain_shared *sds = sd->shared;
+ struct cpumask *span = sched_domain_span(sd);
+ int nid = cpu_to_node(cpumask_first(span));
+ int flags = __GFP_ZERO | GFP_KERNEL;
+ struct sparsemask *mask;
+
+ /*
+ * Allocate the bitmap if not already allocated. This is called for
+ * every CPU in the LLC but only allocates once per sd_llc_shared.
+ */
+ if (!sds->cfs_overload_cpus) {
+ mask = sparsemask_alloc_node(nr_cpu_ids, 3, flags, nid);
+ if (!mask)
+ return 1;
+ sds->cfs_overload_cpus = mask;
+ }

return 0;
}
@@ -1633,7 +1653,8 @@ static void sd_llc_free(struct sched_domain *sd)
if (!sds)
return;

- /* Free data here. Empty for now. */
+ sparsemask_free(sds->cfs_overload_cpus);
+ sds->cfs_overload_cpus = NULL;
}

static int sd_llc_alloc_all(const struct cpumask *cpu_map, struct s_data *d)
--
1.8.3.1
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