[RFC 2/4] sched/numa: replace runnable_load_avg by load_avg

[Vincent Guittot]

Similarly to what has been done for the normal load balance, we can
replace runnable_load_avg by load_avg in numa load balancing and track
other statistics like the utilization and the number of running tasks to
get to better view of the current state of a node.

Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
---
 kernel/sched/fair.c | 102 ++++++++++++++++++++++++++++++++------------
 1 file changed, 75 insertions(+), 27 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a1ea02b5362e..6e4c2b012c48 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1473,38 +1473,35 @@ bool should_numa_migrate_memory(struct task_struct *p, struct page * page,
 	       group_faults_cpu(ng, src_nid) * group_faults(p, dst_nid) * 4;
 }
 
-static inline unsigned long cfs_rq_runnable_load_avg(struct cfs_rq *cfs_rq);
-
-static unsigned long cpu_runnable_load(struct rq *rq)
-{
-	return cfs_rq_runnable_load_avg(&rq->cfs);
-}
+/*
+ * 'numa_type' describes the node at the moment of load balancing.
+ */
+enum numa_type {
+	/* The node has spare capacity that can be used to run more tasks.  */
+	node_has_spare = 0,
+	/*
+	 * The node is fully used and the tasks don't compete for more CPU
+	 * cycles. Nevertheless, some tasks might wait before running.
+	 */
+	node_fully_busy,
+	/*
+	 * The node is overloaded and can't provide expected CPU cycles to all
+	 * tasks.
+	 */
+	node_overloaded
+};
 
 /* Cached statistics for all CPUs within a node */
 struct numa_stats {
 	unsigned long load;
-
+	unsigned long util;
 	/* Total compute capacity of CPUs on a node */
 	unsigned long compute_capacity;
+	unsigned int nr_running;
+	unsigned int weight;
+	enum numa_type node_type;
 };
 
-/*
- * XXX borrowed from update_sg_lb_stats
- */
-static void update_numa_stats(struct numa_stats *ns, int nid)
-{
-	int cpu;
-
-	memset(ns, 0, sizeof(*ns));
-	for_each_cpu(cpu, cpumask_of_node(nid)) {
-		struct rq *rq = cpu_rq(cpu);
-
-		ns->load += cpu_runnable_load(rq);
-		ns->compute_capacity += capacity_of(cpu);
-	}
-
-}
-
 struct task_numa_env {
 	struct task_struct *p;
 
@@ -1521,6 +1518,47 @@ struct task_numa_env {
 	int best_cpu;
 };
 
+static unsigned long cpu_load(struct rq *rq);
+static unsigned long cpu_util(int cpu);
+
+static inline enum
+numa_type numa_classify(unsigned int imbalance_pct,
+			 struct numa_stats *ns)
+{
+	if ((ns->nr_running > ns->weight) &&
+	    ((ns->compute_capacity * 100) < (ns->util * imbalance_pct)))
+		return node_overloaded;
+
+	if ((ns->nr_running < ns->weight) ||
+	    ((ns->compute_capacity * 100) > (ns->util * imbalance_pct)))
+		return node_has_spare;
+
+	return node_fully_busy;
+}
+
+/*
+ * XXX borrowed from update_sg_lb_stats
+ */
+static void update_numa_stats(struct task_numa_env *env,
+			      struct numa_stats *ns, int nid)
+{
+	int cpu;
+
+	memset(ns, 0, sizeof(*ns));
+	for_each_cpu(cpu, cpumask_of_node(nid)) {
+		struct rq *rq = cpu_rq(cpu);
+
+		ns->load += cpu_load(rq);
+		ns->util += cpu_util(cpu);
+		ns->nr_running += rq->cfs.h_nr_running;
+		ns->compute_capacity += capacity_of(cpu);
+	}
+
+	ns->weight = cpumask_weight(cpumask_of_node(nid));
+
+	ns->node_type = numa_classify(env->imbalance_pct, ns);
+}
+
 static void task_numa_assign(struct task_numa_env *env,
 			     struct task_struct *p, long imp)
 {
@@ -1556,6 +1594,11 @@ static bool load_too_imbalanced(long src_load, long dst_load,
 	long orig_src_load, orig_dst_load;
 	long src_capacity, dst_capacity;
 
+
+	/* If dst node has spare capacity, there is no real load imbalance */
+	if (env->dst_stats.node_type == node_has_spare)
+		return false;
+
 	/*
 	 * The load is corrected for the CPU capacity available on each node.
 	 *
@@ -1788,10 +1831,10 @@ static int task_numa_migrate(struct task_struct *p)
 	dist = env.dist = node_distance(env.src_nid, env.dst_nid);
 	taskweight = task_weight(p, env.src_nid, dist);
 	groupweight = group_weight(p, env.src_nid, dist);
-	update_numa_stats(&env.src_stats, env.src_nid);
+	update_numa_stats(&env, &env.src_stats, env.src_nid);
 	taskimp = task_weight(p, env.dst_nid, dist) - taskweight;
 	groupimp = group_weight(p, env.dst_nid, dist) - groupweight;
-	update_numa_stats(&env.dst_stats, env.dst_nid);
+	update_numa_stats(&env, &env.dst_stats, env.dst_nid);
 
 	/* Try to find a spot on the preferred nid. */
 	task_numa_find_cpu(&env, taskimp, groupimp);
@@ -1824,7 +1867,7 @@ static int task_numa_migrate(struct task_struct *p)
 
 			env.dist = dist;
 			env.dst_nid = nid;
-			update_numa_stats(&env.dst_stats, env.dst_nid);
+			update_numa_stats(&env, &env.dst_stats, env.dst_nid);
 			task_numa_find_cpu(&env, taskimp, groupimp);
 		}
 	}
@@ -5446,6 +5489,11 @@ static unsigned long cpu_load_without(struct rq *rq, struct task_struct *p)
 	return load;
 }
 
+static unsigned long cpu_runnable_load(struct rq *rq)
+{
+	return cfs_rq_runnable_load_avg(&rq->cfs);
+}
+
 static unsigned long capacity_of(int cpu)
 {
 	return cpu_rq(cpu)->cpu_capacity;
-- 
2.17.1