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SubjectRe: [PATCH 2/2] x86: speed cpu_up by quirking cpu_init_udelay

* Len Brown <lenb@kernel.org> wrote:

> From: Len Brown <len.brown@intel.com>
>
> Modern processor familes are on a white-list to remove
> the costly cpu_init_udelay 10000. Unknown processor families
> get the traditional 10ms delay in cpu_up().
>
> This seemed more efficient than forcing modern processors
> to exhaustively search a black-list having all the old
> processor families that should have a 10ms delay.
> For not only are new processor familes infrequently added,
> the white list also allows a delay other than 0, if needed.

> static unsigned int init_udelay = UDELAY_10MS_DEFAULT;
>
> +static const struct x86_cpu_id init_udelay_ids[] = {
> + { X86_VENDOR_INTEL, 0x6, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
> + { X86_VENDOR_AMD, 0x16, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
> + { X86_VENDOR_AMD, 0x15, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
> + { X86_VENDOR_AMD, 0x14, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
> + { X86_VENDOR_AMD, 0x12, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
> + { X86_VENDOR_AMD, 0x11, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
> + { X86_VENDOR_AMD, 0x10, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
> + { X86_VENDOR_AMD, 0xF, X86_MODEL_ANY, X86_FEATURE_ANY, 0 },
> + {}
> +};

So since especially AMD likes to iterate the family upwards, why not
make this a simple open ended check:

if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
boot_cpu_data.x86 >= 6 ||
boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
boot_cpu_data.x86 >= 15) {

... 0 delay ...
}

... which is much smaller and more future proof?

Thanks,

Ingo


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