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Message-ID: <1bccae2c1830daab13cf892ecb1ae7c05edd98f2.camel@linux.intel.com>
Date: Mon, 15 Sep 2025 09:44:50 -0700
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: K Prateek Nayak <kprateek.nayak@....com>, Peter Zijlstra
<peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>
Cc: Juri Lelli <juri.lelli@...hat.com>, Dietmar Eggemann
<dietmar.eggemann@....com>, Ben Segall <bsegall@...gle.com>, Mel Gorman
<mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>, Tim Chen
<tim.c.chen@...el.com>, Vincent Guittot <vincent.guittot@...aro.org>, Libo
Chen <libo.chen@...cle.com>, Abel Wu <wuyun.abel@...edance.com>, Len Brown
<len.brown@...el.com>, linux-kernel@...r.kernel.org, Chen Yu
<yu.c.chen@...el.com>, "Gautham R . Shenoy" <gautham.shenoy@....com>, Zhao
Liu <zhao1.liu@...el.com>, Vinicius Costa Gomes <vinicius.gomes@...el.com>,
Arjan Van De Ven <arjan.van.de.ven@...el.com>
Subject: Re: [PATCH v3 1/2] sched: Create architecture specific sched domain
distances
On Fri, 2025-09-12 at 08:53 +0530, K Prateek Nayak wrote:
> 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)
That would exceed 80 characters. So we would still need to move some parameters to a different
line to keep within the limit.
> {
> ...
> }
>
> > {
> > - 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)
Yes, __kfree will be better here.
>
> 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.
Sure.
Thanks for the review.
Tim
>
> Apart from those nitpicks, the changes look good to me. Please feel free
> to include:
>
> Reviewed-by: K Prateek Nayak <kprateek.nayak@....com>
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