Re: [Xen-devel] [PATCH v9 11/23] x86emul: support of AVX512* population count insns

[Jan Beulich <JBeulich@xxxxxxxx>]

On 04.07.2019 20:38, Andrew Cooper wrote:
> On 04/07/2019 15:54, Jan Beulich wrote:
>> On 04.07.2019 16:47, Andrew Cooper wrote:
>>> On 01/07/2019 12:22, Jan Beulich wrote:
>>>> --- a/xen/tools/gen-cpuid.py
>>>> +++ b/xen/tools/gen-cpuid.py
>>>> @@ -268,7 +268,7 @@ def crunch_numbers(state):
>>>>             # AVX512 extensions acting on vectors of bytes/words are made
>>>>             # dependents of AVX512BW (as to requiring wider than 16-bit 
>>>> mask
>>>>             # registers), despite the SDM not formally making this 
>>>> connection.
>>>> -        AVX512BW: [AVX512_BF16, AVX512_VBMI, AVX512_VBMI2],
>>>> +        AVX512BW: [AVX512_BF16, AVX512_BITALG, AVX512_VBMI, AVX512_VBMI2],
>>> BITALG should be after VBMI2, because everything in this table is
>>> ordered by bit number.
>> As said before - there's no ordering by bit number possible here.
> 
> Its perfectly easy.  Each feature has a unique number.

Well, okay, for sub-leaves of the same main leaf I can accept
this. But what sorting do you suggest between basic and extended
leaves?

>> The individual features may live on different (sub)leaves. By
>> what you say BF16 shouldn't be first. The list here clearly is
>> sorted alphabetically, and imo that's the only future proof sorting
>> possible (and also for AVX512F, where I had previously offered to
>> put together a patch to switch to alphabetical ordering, if only we
>> could agree on that).
> 
> In which case I missed it during review.
> 
> This feature matrix is deliberately sorted by feature number in an
> effort to preserve chronology, which is a much more useful way of
> reasoning about feature dependencies.

Except that bit numbers are often, but not always an indication of
chronological order.

While I clearly disagree, for there to be progress here, do you
expect me to re-arrange the dependency list above, i.e. going
beyond your initial request? I certainly object to doing _just_
the originally requested adjustment ...

Jan
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