[RFC PATCH v2 2/3] sched: build schedule balance map

[Michael Wang]

This patch will build schedule balance map as designed, now
cpu_sbm->sd[f][l] can directly locate the sd of cpu on level 'l'
with flag 'f' supported.

In order to quickly locate the lower sd while changing the base cpu,
the level with empty sd in map will be filled with the lower sd.

Signed-off-by: Michael Wang <wangyun@xxxxxxxxxxxxxxxxxx>
---
 kernel/sched/core.c |   70 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 70 insertions(+), 0 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 092c801..0c63303 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5578,6 +5578,62 @@ static void update_top_cache_domain(int cpu)
 static int sbm_max_level;
 DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_balance_map, sbm_array);
 
+static void build_sched_balance_map(int cpu)
+{
+	struct sched_balance_map *sbm = &per_cpu(sbm_array, cpu);
+	struct sched_domain *sd = cpu_rq(cpu)->sd;
+	struct sched_domain *top_sd = NULL;
+	int i, type, level = 0;
+
+	memset(sbm->top_level, 0, sizeof((*sbm).top_level));
+	memset(sbm->affine_map, 0, sizeof((*sbm).affine_map));
+	for (type = 0; type < SBM_MAX_TYPE; type++) {
+		memset(sbm->sd[type], 0,
+			sizeof(struct sched_domain *) * sbm_max_level);
+	}
+
+	while (sd) {
+		if (!(sd->flags & SD_LOAD_BALANCE))
+			continue;
+
+		if (sd->flags & SD_BALANCE_EXEC) {
+			sbm->top_level[SBM_EXEC_TYPE] = sd->level;
+			sbm->sd[SBM_EXEC_TYPE][sd->level] = sd;
+		}
+
+		if (sd->flags & SD_BALANCE_FORK) {
+			sbm->top_level[SBM_FORK_TYPE] = sd->level;
+			sbm->sd[SBM_FORK_TYPE][sd->level] = sd;
+		}
+
+		if (sd->flags & SD_BALANCE_WAKE) {
+			sbm->top_level[SBM_WAKE_TYPE] = sd->level;
+			sbm->sd[SBM_WAKE_TYPE][sd->level] = sd;
+		}
+
+		if (sd->flags & SD_WAKE_AFFINE) {
+			for_each_cpu(i, sched_domain_span(sd)) {
+				if (!sbm->affine_map[i])
+					sbm->affine_map[i] = sd;
+			}
+		}
+
+		sd = sd->parent;
+	}
+
+	/*
+	 * fill the hole to get lower level sd easily.
+	 */
+	for (type = 0; type < SBM_MAX_TYPE; type++) {
+		level = sbm->top_level[type];
+		top_sd = sbm->sd[type][level];
+		if ((++level != sbm_max_level) && top_sd) {
+			for (; level < sbm_max_level; level++)
+				sbm->sd[type][level] = top_sd;
+		}
+	}
+}
+
 /*
  * Attach the domain 'sd' to 'cpu' as its base domain. Callers must
  * hold the hotplug lock.
@@ -5587,6 +5643,9 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
 {
 	struct rq *rq = cpu_rq(cpu);
 	struct sched_domain *tmp;
+	struct sched_balance_map *sbm = &per_cpu(sbm_array, cpu);
+
+	rcu_assign_pointer(rq->sbm, NULL);
 
 	/* Remove the sched domains which do not contribute to scheduling. */
 	for (tmp = sd; tmp; ) {
@@ -5619,6 +5678,17 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu)
 	destroy_sched_domains(tmp, cpu);
 
 	update_top_cache_domain(cpu);
+
+	/* disable sbm if initialization failed or sd detached. */
+	if (!sbm_max_level || !sd)
+		return;
+
+	/*
+	 * synchronize_rcu() is unnecessary here since
+	 * destroy_sched_domains() already do the work.
+	 */
+	build_sched_balance_map(cpu);
+	rcu_assign_pointer(rq->sbm, sbm);
 }
 
 /* cpus with isolated domains */
-- 
1.7.4.1

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