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Re: [PATCH v2 3/3] xen/sched: Make cpu_nr_siblings() architecture-specific
- To: Hirokazu Takahashi <taka@xxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 22 Jun 2026 15:30:44 +0200
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- Cc: Mykyta_Poturai@xxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, George Dunlap <gwd@xxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 22 Jun 2026 13:30:56 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17.06.2026 09:12, Hirokazu Takahashi wrote:
> --- a/xen/arch/x86/include/asm/processor.h
> +++ b/xen/arch/x86/include/asm/processor.h
> @@ -106,6 +106,7 @@ extern void intel_init_arat(void);
>
> #define cpu_to_core(_cpu) (cpu_data[_cpu].cpu_core_id)
> #define cpu_to_socket(_cpu) (cpu_data[_cpu].phys_proc_id)
> +#define cpu_nr_siblings(_cpu) (cpu_data[_cpu].x86_num_siblings)
This is uniformly available when building x86. An earlier patch adds an
#include of the new cpu-topology.h ...
> --- a/xen/common/sched/credit2.c
> +++ b/xen/common/sched/credit2.c
> @@ -29,22 +29,6 @@
> /* #define d2printk printk */
> #define d2printk(x...)
>
> -/*
> - * TODO: Abstract this properly, and figure out what Credit2 wants to do with
> - * the fact that x86_num_siblings doesn't even have the same meaning
> - * between x86 vendors.
> - */
> -static unsigned int cpu_nr_siblings(unsigned int cpu)
> -{
> -#ifdef CONFIG_X86
> - return cpu_data[cpu].x86_num_siblings;
> -#elif defined(CONFIG_CPU_TOPOLOGY)
> - return cpu_topology[cpu].num_siblings;
> -#else
> - return 1;
> -#endif
> -}
... to this file, thus allowing for the static function to be dropped. However,
...
> --- a/xen/include/xen/cpu-topology.h
> +++ b/xen/include/xen/cpu-topology.h
> @@ -24,6 +24,7 @@ void 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)
> +#define cpu_nr_siblings(cpu) (cpu_topology[cpu].num_siblings)
>
> #else /* CONFIG_CPU_TOPOLOGY */
>
> @@ -31,6 +32,7 @@ static inline void init_cpu_topology(void) {}
>
> #define cpu_to_core(cpu) (0U)
> #define cpu_to_socket(cpu) (0U)
> +#define cpu_nr_siblings(cpu) (1U)
>
> #endif /* CONFIG_CPU_TOPOLOGY */
... one of the two #define-s will take effect here. Whichever one it is, it'll
conflict with x86'es (when building for x86). Am I overlooking something here,
or did you simply not build-test x86? Looks like a problem of the same kind
may actually be introduced already by patch 2.
Jan
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