Re: [PATCH v3 07/34] x86/hyperv: Introduce HV_MAX_SPARSE_VCPU_BANKS/HV_VCPUS_PER_SPARSE_BANK constants

[Wei Liu]

On Thu, Apr 14, 2022 at 03:19:46PM +0200, Vitaly Kuznetsov wrote:
> It may not come clear from where the magical '64' value used in
> __cpumask_to_vpset() come from. Moreover, '64' means both the maximum
> sparse bank number as well as the number of vCPUs per bank. Add defines
> to make things clear. These defines are also going to be used by KVM.
> 
> No functional change.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
>  include/asm-generic/hyperv-tlfs.h |  5 +++++
>  include/asm-generic/mshyperv.h    | 11 ++++++-----
>  2 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
> index fdce7a4cfc6f..020ca9bdbb79 100644
> --- a/include/asm-generic/hyperv-tlfs.h
> +++ b/include/asm-generic/hyperv-tlfs.h
> @@ -399,6 +399,11 @@ struct hv_vpset {
>  	u64 bank_contents[];
>  } __packed;
>  
> +/* The maximum number of sparse vCPU banks which can be encoded by 'struct hv_vpset' */
> +#define HV_MAX_SPARSE_VCPU_BANKS (64)
> +/* The number of vCPUs in one sparse bank */
> +#define HV_VCPUS_PER_SPARSE_BANK (64)

I think replacing the magic number with a macro is a good thing.

Where do you get these names? Did you make them up yourself?

I'm trying to dig into internal code to find the most appropriate names,
but I couldn't find any so far. Michael, do you have insight here?

Thanks,
Wei.