Re: [PATCH 2/3] xen/sched: Link CPU topology to scheduler

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.06.2026 13:13, Hirokazu Takahashi wrote:
> Make CPU topology information available to the Xen scheduler.
> Additionally, ensure that this topology information is displayed
> when executing the 'xl info -n' command.

Both in title and description you're pretty generic, yet then ...

>  xen/arch/arm/include/asm/processor.h  |  4 ---
>  xen/arch/arm/smpboot.c                | 10 ++++--
>  xen/common/device-tree/cpu-topology.c | 51 +++++++++++++++++++++++++++
>  xen/common/sched/credit2.c            |  3 ++
>  xen/common/sysctl.c                   |  1 +
>  xen/include/xen/cpu-topology.h        | 10 ++++++
>  6 files changed, 72 insertions(+), 7 deletions(-)

... only the credit2 scheduler is actually enabled.
> --- a/xen/common/device-tree/cpu-topology.c
> +++ b/xen/common/device-tree/cpu-topology.c
> @@ -325,6 +325,55 @@ int __init parse_dt_topology(void)
>      return parse_socket(map);
>  }
>  
> +static void __init setup_cpu_topology_ids(void)
> +{
> +    unsigned int cpu;
> +    unsigned int next_core_id = 0U;
> +    unsigned int next_cluster_id = 0U;
> +    unsigned int next_socket_id = 0U;
> +
> +    for_each_possible_cpu( cpu )

Nit (style): Either you deem for_each_possible_cpu a (pseudo-)keyword
(then there's a blank missing) or you don't (then there are excess
blanks).

> +    {
> +        unsigned int first_cpu;
> +        struct cpu_topology *topo = &cpu_topology[cpu];
> +
> +        first_cpu = cpumask_first(&topo->thread_sibling);
> +        if ( first_cpu == cpu )
> +        {
> +            topo->phys_core_id = next_core_id;
> +            next_core_id++;
> +        }
> +        else
> +        {
> +            topo->phys_core_id = cpu_topology[first_cpu].phys_core_id;
> +        }

Nit, here and below: Please omit unnecessary figure braces.

> @@ -339,4 +388,6 @@ void __init dt_init_cpu_topology(void)
>  
>      for_each_possible_cpu( cpu )
>          setup_siblings_masks(cpu);
As to the earlier remark: Bad pre-existing examples don't count.

> @@ -19,11 +23,17 @@ extern struct cpu_topology *cpu_topology;
>  void map_cpuid_to_node(unsigned int cpuid, struct dt_device_node *cpu_node);
>  void dt_init_cpu_topology(void);
>  
> +#define cpu_to_core(_cpu)   (cpu_topology[_cpu].phys_core_id)
> +#define cpu_to_socket(_cpu)   (cpu_topology[_cpu].phys_socket_id)

Please can you avoid introducing new name space violations (identifiers
with leading underscores should name file scope entities); also again
below.

Jan