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-rw-r--r--kernel/sched/core.c39
1 files changed, 38 insertions, 1 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4b4a63d..536b213 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6024,6 +6024,11 @@ static void destroy_sched_domains(struct sched_domain *sd, int cpu)
* SD_SHARE_PKG_RESOURCE set (Last Level Cache Domain) for this
* allows us to avoid some pointer chasing select_idle_sibling().
*
+ * Iterate domains and sched_groups downward, assigning CPUs to be
+ * select_idle_sibling() hw buddy. Cross-wiring hw makes bouncing
+ * due to random perturbation self canceling, ie sw buddies pull
+ * their counterpart to their CPU's hw counterpart.
+ *
* Also keep a unique ID per domain (we use the first cpu number in
* the cpumask of the domain), this allows us to quickly tell if
* two cpus are in the same cache domain, see cpus_share_cache().
@@ -6037,8 +6042,40 @@ static void update_top_cache_domain(int cpu)
int id = cpu;
sd = highest_flag_domain(cpu, SD_SHARE_PKG_RESOURCES);
- if (sd)
+ if (sd) {
+ struct sched_domain *tmp = sd;
+ struct sched_group *sg, *prev;
+ bool right;
+
+ /*
+ * Traverse to first CPU in group, and count hops
+ * to cpu from there, switching direction on each
+ * hop, never ever pointing the last CPU rightward.
+ */
+ do {
+ id = cpumask_first(sched_domain_span(tmp));
+ prev = sg = tmp->groups;
+ right = 1;
+
+ while (cpumask_first(sched_group_cpus(sg)) != id)
+ sg = sg->next;
+
+ while (!cpumask_test_cpu(cpu, sched_group_cpus(sg))) {
+ prev = sg;
+ sg = sg->next;
+ right = !right;
+ }
+
+ /* A CPU went down, never point back to domain start. */
+ if (right && cpumask_first(sched_group_cpus(sg->next)) == id)
+ right = false;
+
+ sg = right ? sg->next : prev;
+ tmp->idle_buddy = cpumask_first(sched_group_cpus(sg));
+ } while ((tmp = tmp->child));
+
id = cpumask_first(sched_domain_span(sd));
+ }
rcu_assign_pointer(per_cpu(sd_llc, cpu), sd);
per_cpu(sd_llc_id, cpu) = id;
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