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

[Julien Grall <julien@xxxxxxx>]

Hi,

On 10/06/2026 12:13, 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.
>
> Signed-off-by: Hirokazu Takahashi <taka@xxxxxxxxxxxxx>
> ---
>   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(-)
>
> diff --git a/xen/arch/arm/include/asm/processor.h 
> b/xen/arch/arm/include/asm/processor.h
> index a3753c317f..41fa73cfc4 100644
> --- a/xen/arch/arm/include/asm/processor.h
> +++ b/xen/arch/arm/include/asm/processor.h
> @@ -613,10 +613,6 @@ void show_stack(const struct cpu_user_regs *regs);
>   
>   #define cpu_relax() barrier() /* Could yield? */
>   
> -/* All a bit UP for the moment */
> -#define cpu_to_core(_cpu)   (0)
> -#define cpu_to_socket(_cpu) (0)
> -
>   struct vcpu;
>   void vcpu_regs_hyp_to_user(const struct vcpu *vcpu,
>                              struct vcpu_guest_core_regs *regs);
> diff --git a/xen/arch/arm/smpboot.c b/xen/arch/arm/smpboot.c
> index c071f1494f..b25d98c109 100644
> --- a/xen/arch/arm/smpboot.c
> +++ b/xen/arch/arm/smpboot.c
> @@ -91,13 +91,17 @@ static int setup_cpu_sibling_map(int cpu)
>            !zalloc_cpumask_var(&per_cpu(cpu_core_mask, cpu)) )
>           return -ENOMEM;
>   
> +#ifdef CONFIG_DT_CPU_TOPOLOGY
For Arm, we support both ACPI and Device-Tree in a single binary. That's 
fine if we don't support NUMA with ACPI for now, but we need to make 
sure this doesn't regress for now.
With that in mind, I was expecting some runtime checks based on whether 
ACPI or DT is used. Can you explain why this is not the case?
Cheers,

--
Julien Grall