[PATCH v4 03/10] sched/topology: Provide cfs_overload_cpus bitmap

[Steve Sistare]

From: Steve Sistare <steve.sist...@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.sist...@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