Re: [Xen-devel] [PATCH v4] x86/cpuid: AVX-512 Feature Detection

["Kang, Luwei" <luwei.kang@xxxxxxxxx>]

What about remove the dependency between AVX2 and AVX512F ( AVX2: [AVX512F], ) ?


-----Original Message-----
From: Jan Beulich [mailto:JBeulich@xxxxxxxx] 
Sent: Friday, July 1, 2016 3:56 PM
To: andrew.cooper3@xxxxxxxxxx; Kang, Luwei <luwei.kang@xxxxxxxxx>
Cc: chao.p.peng@xxxxxxxxxxxxxxx; xen-devel@xxxxxxxxxxxxx
Subject: Re: [PATCH v4] x86/cpuid: AVX-512 Feature Detection

>>> On 30.06.16 at 07:50, <luwei.kang@xxxxxxxxx> wrote:
> --- a/xen/tools/gen-cpuid.py
> +++ b/xen/tools/gen-cpuid.py
> @@ -243,6 +243,17 @@ def crunch_numbers(state):
>          # AMD K6-2+ and K6-III processors shipped with 3DNow+, beyond the
>          # standard 3DNow in the earlier K6 processors.
>          _3DNOW: [_3DNOWEXT],
> +
> +        # AVX2 is an extension to AVX, providing mainly new integer 
> instructions.
> +        # In principle, AVX512 only takes YMM register state as a 
> prerequisite
> +        # and many AVX2 instructions are extended by AVX512F to 512-bit 
> forms.
> +        AVX2: [AVX512F],

I think this was meant to be "but" or "yet" instead of "and". And then I'm not 
particularly happy about the asymmetry with AVX (which is not dependent on SSE 
or any of its successors, despite extending many of them to 256-bit forms). 
Plus e.g. FMA gets extended too, but isn't being made a dependency. And quite 
opposite to that, at least some AVX2 instructions get extended only by e.g. 
AVX512BW.
Nor are any of the extended forms listed to require other than the
AVX512* bits checked in the doc.

Jan


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