Re: [PATCH v4 1/9] sched/topology: Compute sd_weight considering cpuset partitions

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Mar 12, 2026 at 04:44:26AM +0000, K Prateek Nayak wrote:
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 061f8c85f555..34b20b0e1867 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -1645,8 +1645,6 @@ sd_init(struct sched_domain_topology_level *tl,
>  	struct cpumask *sd_span;
>  	u64 now = sched_clock();
>  
> -	sd_weight = cpumask_weight(tl->mask(tl, cpu));
> -
>  	if (tl->sd_flags)
>  		sd_flags = (*tl->sd_flags)();
>  	if (WARN_ONCE(sd_flags & ~TOPOLOGY_SD_FLAGS,
> @@ -1654,8 +1652,6 @@ sd_init(struct sched_domain_topology_level *tl,
>  		sd_flags &= TOPOLOGY_SD_FLAGS;
>  
>  	*sd = (struct sched_domain){
> -		.min_interval		= sd_weight,
> -		.max_interval		= 2*sd_weight,
>  		.busy_factor		= 16,
>  		.imbalance_pct		= 117,
>  
> @@ -1675,7 +1671,6 @@ sd_init(struct sched_domain_topology_level *tl,
>  					,
>  
>  		.last_balance		= jiffies,
> -		.balance_interval	= sd_weight,
>  
>  		/* 50% success rate */
>  		.newidle_call		= 512,
> @@ -1693,6 +1688,11 @@ sd_init(struct sched_domain_topology_level *tl,
>  	cpumask_and(sd_span, cpu_map, tl->mask(tl, cpu));
>  	sd_id = cpumask_first(sd_span);
>  
> +	sd_weight = cpumask_weight(sd_span);
> +	sd->min_interval = sd_weight;
> +	sd->max_interval = 2 * sd_weight;
> +	sd->balance_interval = sd_weight;
> +
>  	sd->flags |= asym_cpu_capacity_classify(sd_span, cpu_map);
>  
>  	WARN_ONCE((sd->flags & (SD_SHARE_CPUCAPACITY | SD_ASYM_CPUCAPACITY)) ==


Why not like so?

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 061f8c85f555..79bab80af8f2 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1645,13 +1645,17 @@ sd_init(struct sched_domain_topology_level *tl,
 	struct cpumask *sd_span;
 	u64 now = sched_clock();
 
-	sd_weight = cpumask_weight(tl->mask(tl, cpu));
+	sd_span = sched_domain_span(sd);
+	cpumask_and(sd_span, cpu_map, tl->mask(tl, cpu));
+	sd_weight = cpumask_weight(sd_span);
+	sd_id = cpumask_first(sd_span);
 
 	if (tl->sd_flags)
 		sd_flags = (*tl->sd_flags)();
 	if (WARN_ONCE(sd_flags & ~TOPOLOGY_SD_FLAGS,
-			"wrong sd_flags in topology description\n"))
+		      "wrong sd_flags in topology description\n"))
 		sd_flags &= TOPOLOGY_SD_FLAGS;
+	sd_flags |= asym_cpu_capacity_classify(sd_span, cpu_map);
 
 	*sd = (struct sched_domain){
 		.min_interval		= sd_weight,
@@ -1689,12 +1693,6 @@ sd_init(struct sched_domain_topology_level *tl,
 		.name			= tl->name,
 	};
 
-	sd_span = sched_domain_span(sd);
-	cpumask_and(sd_span, cpu_map, tl->mask(tl, cpu));
-	sd_id = cpumask_first(sd_span);
-
-	sd->flags |= asym_cpu_capacity_classify(sd_span, cpu_map);
-
 	WARN_ONCE((sd->flags & (SD_SHARE_CPUCAPACITY | SD_ASYM_CPUCAPACITY)) ==
 		  (SD_SHARE_CPUCAPACITY | SD_ASYM_CPUCAPACITY),
 		  "CPU capacity asymmetry not supported on SMT\n");