Re: [PATCH v3 1/2] sched: Create architecture specific sched domain distances

[K Prateek Nayak <kprateek.nayak@amd.com>]

Hello Tim,

On 9/12/2025 12:00 AM, Tim Chen wrote:
> +static int sched_record_numa_dist(int offline_node, int (*n_dist)(int, int),
> +		int **dist, int *levels)
> +

nit. Is the blank line above intentional?

Also personally I prefer breaking the two lines above as:

static int
sched_record_numa_dist(int offline_node, int (*n_dist)(int, int), int **dist, int *levels)
{
	...
}

>  {
> -	struct sched_domain_topology_level *tl;
>  	unsigned long *distance_map;

Since we are breaking this out and adding return values, can we also
cleanup that bitmap_free() before every return with __free(bitmap) like:

(Only build tested)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 6c0ff62322cb..baa79e79ced8 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1910,9 +1910,8 @@ static int numa_node_dist(int i, int j)
 
 static int sched_record_numa_dist(int offline_node, int (*n_dist)(int, int),
 		int **dist, int *levels)
-
 {
-	unsigned long *distance_map;
+	unsigned long *distance_map __free(bitmap) = NULL;
 	int nr_levels = 0;
 	int i, j;
 	int *distances;
@@ -1932,7 +1931,6 @@ static int sched_record_numa_dist(int offline_node, int (*n_dist)(int, int),
 
 			if (distance < LOCAL_DISTANCE || distance >= NR_DISTANCE_VALUES) {
 				sched_numa_warn("Invalid distance value range");
-				bitmap_free(distance_map);
 				return -EINVAL;
 			}
 
@@ -1946,19 +1944,17 @@ static int sched_record_numa_dist(int offline_node, int (*n_dist)(int, int),
 	nr_levels = bitmap_weight(distance_map, NR_DISTANCE_VALUES);
 
 	distances = kcalloc(nr_levels, sizeof(int), GFP_KERNEL);
-	if (!distances) {
-		bitmap_free(distance_map);
+	if (!distances)
 		return -ENOMEM;
-	}
+
 	for (i = 0, j = 0; i < nr_levels; i++, j++) {
 		j = find_next_bit(distance_map, NR_DISTANCE_VALUES, j);
 		distances[i] = j;
 	}
+
 	*dist = distances;
 	*levels = nr_levels;
 
-	bitmap_free(distance_map);
-
 	return 0;
 }
 
---

>  	int nr_levels = 0;
>  	int i, j;
>  	int *distances;
> -	struct cpumask ***masks;
>  
>  	/*
>  	 * O(nr_nodes^2) de-duplicating selection sort -- in order to find the
> @@ -1902,17 +1923,17 @@ void sched_init_numa(int offline_node)
>  	 */
>  	distance_map = bitmap_alloc(NR_DISTANCE_VALUES, GFP_KERNEL);
>  	if (!distance_map)
> -		return;
> +		return -ENOMEM;
>  
>  	bitmap_zero(distance_map, NR_DISTANCE_VALUES);
>  	for_each_cpu_node_but(i, offline_node) {
>  		for_each_cpu_node_but(j, offline_node) {
> -			int distance = node_distance(i, j);
> +			int distance = n_dist(i, j);
>  
>  			if (distance < LOCAL_DISTANCE || distance >= NR_DISTANCE_VALUES) {
>  				sched_numa_warn("Invalid distance value range");
>  				bitmap_free(distance_map);
> -				return;
> +				return -EINVAL;
>  			}
>  
>  			bitmap_set(distance_map, distance, 1);
> @@ -1927,17 +1948,66 @@ void sched_init_numa(int offline_node)
>  	distances = kcalloc(nr_levels, sizeof(int), GFP_KERNEL);
>  	if (!distances) {
>  		bitmap_free(distance_map);
> -		return;
> +		return -ENOMEM;
>  	}
> -
>  	for (i = 0, j = 0; i < nr_levels; i++, j++) {
>  		j = find_next_bit(distance_map, NR_DISTANCE_VALUES, j);
>  		distances[i] = j;
>  	}
> -	rcu_assign_pointer(sched_domains_numa_distance, distances);
> +	*dist = distances;
> +	*levels = nr_levels;
>  
>  	bitmap_free(distance_map);
>  
> +	return 0;
> +}
> +
> +static int avg_remote_numa_distance(int offline_node)
> +{
> +	int i, j;
> +	int distance, nr_remote = 0, total_distance = 0;
> +
> +	for_each_cpu_node_but(i, offline_node) {
> +		for_each_cpu_node_but(j, offline_node) {
> +			distance = node_distance(i, j);
> +
> +			if (distance >= REMOTE_DISTANCE) {
> +				nr_remote++;
> +				total_distance += distance;
> +			}
> +		}
> +	}
> +	if (nr_remote)
> +		return total_distance / nr_remote;
> +	else
> +		return REMOTE_DISTANCE;
> +}
> +
> +void sched_init_numa(int offline_node)
> +{
> +	struct sched_domain_topology_level *tl;
> +	int nr_levels, nr_node_levels;
> +	int i, j;
> +	int *distances, *domain_distances;
> +	struct cpumask ***masks;
> +
> +	if (sched_record_numa_dist(offline_node, numa_node_dist, &distances,
> +				   &nr_node_levels))
> +		return;
> +
> +	WRITE_ONCE(sched_avg_remote_numa_distance,
> +		   avg_remote_numa_distance(offline_node));

nit.

Can add a small comment here saying arch_sched_node_distance() may
depend on sched_avg_remote_numa_distance and requires it to be
initialized correctly before computing domain_distances.

Apart from those nitpicks, the changes look good to me. Please feel free
to include:

Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>

-- 
Thanks and Regards,
Prateek

> +
> +	if (sched_record_numa_dist(offline_node,
> +				   arch_sched_node_distance, &domain_distances,
> +				   &nr_levels)) {
> +		kfree(distances);
> +		return;
> +	}
> +	rcu_assign_pointer(sched_numa_node_distance, distances);
> +	WRITE_ONCE(sched_max_numa_distance, distances[nr_node_levels - 1]);
> +	WRITE_ONCE(sched_numa_node_levels, nr_node_levels);
> +
>  	/*
>  	 * 'nr_levels' contains the number of unique distances
>  	 *