Use the MADT and SRAT table data to compute __num_nodes_per_package.

This number is useful to divinate the various Intel CoD/SNC modes,
since the platforms are failing to provide this otherwise.

Doing it this way is independent of the number of online CPUs and
other such shenanigans.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 arch/x86/include/asm/topology.h |    1 +
 arch/x86/kernel/cpu/common.c    |    3 +++
 arch/x86/kernel/cpu/topology.c  |    9 ++++++++-
 3 files changed, 12 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -158,6 +158,7 @@ extern unsigned int __max_logical_packag
 extern unsigned int __max_threads_per_core;
 extern unsigned int __num_threads_per_package;
 extern unsigned int __num_cores_per_package;
+extern unsigned int __num_nodes_per_package;
 
 const char *get_topology_cpu_type_name(struct cpuinfo_x86 *c);
 enum x86_topology_cpu_type get_topology_cpu_type(struct cpuinfo_x86 *c);
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -95,6 +95,9 @@ EXPORT_SYMBOL(__max_dies_per_package);
 unsigned int __max_logical_packages __ro_after_init = 1;
 EXPORT_SYMBOL(__max_logical_packages);
 
+unsigned int __num_nodes_per_package __ro_after_init = 1;
+EXPORT_SYMBOL(__num_nodes_per_package);
+
 unsigned int __num_cores_per_package __ro_after_init = 1;
 EXPORT_SYMBOL(__num_cores_per_package);
 
--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -497,11 +497,18 @@ void __init topology_init_possible_cpus(
 	set_nr_cpu_ids(allowed);
 
 	cnta = domain_weight(TOPO_PKG_DOMAIN);
+	cntb = domain_weight(TOPO_NUMA_DOMAIN);
+
+	__num_nodes_per_package = DIV_ROUND_UP(cntb, cnta);
+
+	pr_info("Max. logical packages: %3u\n", cnta);
+	pr_info("Max. logical nodes:    %3u\n", cntb);
+	pr_info("Num. nodes per package:%3u\n", __num_nodes_per_package);
+
 	cntb = domain_weight(TOPO_DIE_DOMAIN);
 	__max_logical_packages = cnta;
 	__max_dies_per_package = 1U << (get_count_order(cntb) - get_count_order(cnta));
 
-	pr_info("Max. logical packages: %3u\n", cnta);
 	pr_info("Max. logical dies:     %3u\n", cntb);
 	pr_info("Max. dies per package: %3u\n", __max_dies_per_package);

On Thu, Feb 26, 2026 at 11:49:12AM +0100, Peter Zijlstra wrote:
> Use the MADT and SRAT table data to compute __num_nodes_per_package.
> 
> This number is useful to divinate the various Intel CoD/SNC modes,
> since the platforms are failing to provide this otherwise.
> 
> Doing it this way is independent of the number of online CPUs and
> other such shenanigans.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  arch/x86/include/asm/topology.h |    1 +
>  arch/x86/kernel/cpu/common.c    |    3 +++
>  arch/x86/kernel/cpu/topology.c  |    9 ++++++++-
>  3 files changed, 12 insertions(+), 1 deletion(-)
> 
> --- a/arch/x86/include/asm/topology.h
> +++ b/arch/x86/include/asm/topology.h
> @@ -158,6 +158,7 @@ extern unsigned int __max_logical_packag
>  extern unsigned int __max_threads_per_core;
>  extern unsigned int __num_threads_per_package;
>  extern unsigned int __num_cores_per_package;
> +extern unsigned int __num_nodes_per_package;
>  
>  const char *get_topology_cpu_type_name(struct cpuinfo_x86 *c);
>  enum x86_topology_cpu_type get_topology_cpu_type(struct cpuinfo_x86 *c);
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -95,6 +95,9 @@ EXPORT_SYMBOL(__max_dies_per_package);
>  unsigned int __max_logical_packages __ro_after_init = 1;
>  EXPORT_SYMBOL(__max_logical_packages);
>  
> +unsigned int __num_nodes_per_package __ro_after_init = 1;
> +EXPORT_SYMBOL(__num_nodes_per_package);
> +
>  unsigned int __num_cores_per_package __ro_after_init = 1;
>  EXPORT_SYMBOL(__num_cores_per_package);
>  
> --- a/arch/x86/kernel/cpu/topology.c
> +++ b/arch/x86/kernel/cpu/topology.c
> @@ -497,11 +497,18 @@ void __init topology_init_possible_cpus(
>  	set_nr_cpu_ids(allowed);
>  
>  	cnta = domain_weight(TOPO_PKG_DOMAIN);
> +	cntb = domain_weight(TOPO_NUMA_DOMAIN);

We'll need to check CONFIG_NUMA here.

TOPO_NUMA_DOMAIN is undeclared when CONFIG_NUMA is not set.

> +
> +	__num_nodes_per_package = DIV_ROUND_UP(cntb, cnta);
> +
> +	pr_info("Max. logical packages: %3u\n", cnta);
> +	pr_info("Max. logical nodes:    %3u\n", cntb);
> +	pr_info("Num. nodes per package:%3u\n", __num_nodes_per_package);
> +
>  	cntb = domain_weight(TOPO_DIE_DOMAIN);
>  	__max_logical_packages = cnta;
>  	__max_dies_per_package = 1U << (get_count_order(cntb) - get_count_order(cnta));
>  
> -	pr_info("Max. logical packages: %3u\n", cnta);
>  	pr_info("Max. logical dies:     %3u\n", cntb);
>  	pr_info("Max. dies per package: %3u\n", __max_dies_per_package);
>  
> 
>

On Thu, Feb 26, 2026 at 11:46:15AM -0600, Kyle Meyer wrote:

> > --- a/arch/x86/kernel/cpu/topology.c
> > +++ b/arch/x86/kernel/cpu/topology.c
> > @@ -497,11 +497,18 @@ void __init topology_init_possible_cpus(
> >  	set_nr_cpu_ids(allowed);
> >  
> >  	cnta = domain_weight(TOPO_PKG_DOMAIN);
> > +	cntb = domain_weight(TOPO_NUMA_DOMAIN);
> 
> We'll need to check CONFIG_NUMA here.
> 
> TOPO_NUMA_DOMAIN is undeclared when CONFIG_NUMA is not set.

Indeed.