Re: [PATCH v2 2/8] x86/resctrl: Add RESCTRL_NPS_NODE scope for AMD NPS-aligned domains

[Peter Newman]

Hi Babu,

On Fri, Apr 24, 2026 at 3:42 AM Babu Moger <babu.moger@xxxxxxx> wrote:
>
> Global Memory Bandwidth Allocation (GMBA) control domains on AMD follow the
> Nodes Per Socket (NPS) configuration. With NPS 4 there is a single domain
> per package; otherwise the domain aligns with the NUMA node.
>
> By default, all QOS Domains in the system are included in a single GLBE
> Control Domain. However, BIOS options may establish several GLBE Control
> Domains within the system using NPS configuration. When configured, each
> NUMA node functions as an individual GLBE domain, except when the system is
> configured in NPS=4 mode in which case only a single GLBE domain exists
> which contains all QOS Domains in the system.

The previous paragraph said NPS 4 is a single domain per package, not
system-wide.

>
> Add RESCTRL_NPS_NODE to enum resctrl_scope and implement
> get_domain_id_nps().
>
> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> ---
> v2: Add RESCTRL_NPS_NODE scope to add support for NPS-aligned resource.
> ---
>  arch/x86/kernel/cpu/resctrl/core.c | 20 ++++++++++++++++++++
>  include/linux/resctrl.h            |  1 +
>  2 files changed, 21 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
> index 269265d98ad7..0f58f5e3b853 100644
> --- a/arch/x86/kernel/cpu/resctrl/core.c
> +++ b/arch/x86/kernel/cpu/resctrl/core.c
> @@ -451,6 +451,24 @@ static int l3_mon_domain_mbm_alloc(u32 num_rmid, struct rdt_hw_l3_mon_domain *hw
>         return -ENOMEM;
>  }
>
> +/**
> + * get_domain_id_nps() - Domain id for %RESCTRL_NPS_NODE (AMD NPS / GMBA)
> + * @cpu:       CPU to query.
> + *
> + * Global memory bandwidth allocation (GMBA) control domains on AMD follow
> + * the socket NPS layout. With NPS 4 there is a single control domain per
> + * package, so every CPU maps to domain id 0. For other NPS settings the
> + * domain matches the CPU's NUMA node.
> + *
> + * Return: 0 when NPS is 4, otherwise the NUMA node id for @cpu.
> + */
> +static int get_domain_id_nps(int cpu)
> +{
> +       if (topology_num_nodes_per_package() == 4)
> +               return 0;

ID is 0 regardless of the number of packages, unlike the
RESCTRL_PACKAGE case below?

> +       return cpu_to_node(cpu);
> +}
> +
>  static int get_domain_id_from_scope(int cpu, enum resctrl_scope scope)
>  {
>         switch (scope) {
> @@ -459,6 +477,8 @@ static int get_domain_id_from_scope(int cpu, enum resctrl_scope scope)
>                 return get_cpu_cacheinfo_id(cpu, scope);
>         case RESCTRL_L3_NODE:
>                 return cpu_to_node(cpu);
> +       case RESCTRL_NPS_NODE:
> +               return get_domain_id_nps(cpu);
>         case RESCTRL_PACKAGE:
>                 return topology_physical_package_id(cpu);
>         default:
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 006e57fd7ca5..80290ded0b82 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -271,6 +271,7 @@ enum resctrl_scope {
>         RESCTRL_L2_CACHE = 2,
>         RESCTRL_L3_CACHE = 3,
>         RESCTRL_L3_NODE,
> +       RESCTRL_NPS_NODE,
>         RESCTRL_PACKAGE,
>  };
>
> --
> 2.43.0
>