sched/topology: Export asym_cap_list

So that we can use it to iterate through available capacities in the
system. Sort asym_cap_list in descending order as expected users are
likely to be interested on the highest capacity first.

Make the list RCU protected to allow for cheap access in hot paths.

Signed-off-by: Qais Yousef <qyousef@layalina.io>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20240324004552.999936-2-qyousef@layalina.io

1 files changed, 25 insertions, 18 deletions

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 99ea5986038c..44ed3d0812ab 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1330,23 +1330,12 @@ next:
 }
 
 /*
- * Asymmetric CPU capacity bits
- */
-struct asym_cap_data {
-	struct list_head link;
-	unsigned long capacity;
-	unsigned long cpus[];
-};
-
-/*
  * Set of available CPUs grouped by their corresponding capacities
  * Each list entry contains a CPU mask reflecting CPUs that share the same
  * capacity.
  * The lifespan of data is unlimited.
  */
-static LIST_HEAD(asym_cap_list);
-
-#define cpu_capacity_span(asym_data) to_cpumask((asym_data)->cpus)
+LIST_HEAD(asym_cap_list);
 
 /*
  * Verify whether there is any CPU capacity asymmetry in a given sched domain.
@@ -1386,21 +1375,39 @@ asym_cpu_capacity_classify(const struct cpumask *sd_span,
 
 }
 
+static void free_asym_cap_entry(struct rcu_head *head)
+{
+	struct asym_cap_data *entry = container_of(head, struct asym_cap_data, rcu);
+	kfree(entry);
+}
+
 static inline void asym_cpu_capacity_update_data(int cpu)
 {
 	unsigned long capacity = arch_scale_cpu_capacity(cpu);
-	struct asym_cap_data *entry = NULL;
+	struct asym_cap_data *insert_entry = NULL;
+	struct asym_cap_data *entry;
 
+	/*
+	 * Search if capacity already exits. If not, track which the entry
+	 * where we should insert to keep the list ordered descendingly.
+	 */
 	list_for_each_entry(entry, &asym_cap_list, link) {
 		if (capacity == entry->capacity)
 			goto done;
+		else if (!insert_entry && capacity > entry->capacity)
+			insert_entry = list_prev_entry(entry, link);
 	}
 
 	entry = kzalloc(sizeof(*entry) + cpumask_size(), GFP_KERNEL);
 	if (WARN_ONCE(!entry, "Failed to allocate memory for asymmetry data\n"))
 		return;
 	entry->capacity = capacity;
-	list_add(&entry->link, &asym_cap_list);
+
+	/* If NULL then the new capacity is the smallest, add last. */
+	if (!insert_entry)
+		list_add_tail_rcu(&entry->link, &asym_cap_list);
+	else
+		list_add_rcu(&entry->link, &insert_entry->link);
 done:
 	__cpumask_set_cpu(cpu, cpu_capacity_span(entry));
 }
@@ -1423,8 +1430,8 @@ static void asym_cpu_capacity_scan(void)
 
 	list_for_each_entry_safe(entry, next, &asym_cap_list, link) {
 		if (cpumask_empty(cpu_capacity_span(entry))) {
-			list_del(&entry->link);
-			kfree(entry);
+			list_del_rcu(&entry->link);
+			call_rcu(&entry->rcu, free_asym_cap_entry);
 		}
 	}
 
@@ -1434,8 +1441,8 @@ static void asym_cpu_capacity_scan(void)
 	 */
 	if (list_is_singular(&asym_cap_list)) {
 		entry = list_first_entry(&asym_cap_list, typeof(*entry), link);
-		list_del(&entry->link);
-		kfree(entry);
+		list_del_rcu(&entry->link);
+		call_rcu(&entry->rcu, free_asym_cap_entry);
 	}
 }