Re: [PATCH v2] Support Intel AVX10.1

[Jan Beulich <jbeulich@suse.com>]

On 23.08.2023 08:25, Jiang, Haochen wrote:
>> -----Original Message-----
>> From: Jan Beulich <jbeulich@suse.com>
>> Sent: Wednesday, August 23, 2023 2:24 PM
>> To: Jiang, Haochen <haochen.jiang@intel.com>
>> Cc: hjl.tools@gmail.com; binutils@sourceware.org
>> Subject: Re: [PATCH v2] Support Intel AVX10.1
>>
>> On 23.08.2023 08:21, Jiang, Haochen wrote:
>>>> -----Original Message-----
>>>> From: Jan Beulich <jbeulich@suse.com>
>>>> Sent: Wednesday, August 23, 2023 1:54 PM
>>>> To: Jiang, Haochen <haochen.jiang@intel.com>
>>>> Cc: hjl.tools@gmail.com; binutils@sourceware.org
>>>> Subject: Re: [PATCH v2] Support Intel AVX10.1
>>>>
>>>> On 23.08.2023 04:20, Jiang, Haochen wrote:
>>>>>
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Jan Beulich <jbeulich@suse.com>
>>>>>> Sent: Friday, August 18, 2023 9:03 PM
>>>>>> To: Jiang, Haochen <haochen.jiang@intel.com>
>>>>>> Cc: hjl.tools@gmail.com; binutils@sourceware.org
>>>>>> Subject: Re: [PATCH v2] Support Intel AVX10.1
>>>>>>
>>>>>> On 14.08.2023 08:45, Haochen Jiang wrote:
>>>>>>> @@ -1315,6 +1321,20 @@ output_i386_opcode (FILE *table, const
>> char
>>>>>> *name, char *str,
>>>>>>>    ident = mkident (name);
>>>>>>>    fprintf (table, "  { MN_%s, 0x%0*llx%s, %u,",
>>>>>>>  	   ident, 2 * (int)length, opcode, end, i);
>>>>>>> +
>>>>>>> +  j = strlen(ident);
>>>>>>> +  /* All AVX512F based instructions are usable for AVX10.1 except
>>>>>>> +     AVX512PF/ER/4FMAPS/4VNNIW/VP2INTERSECT.  */  if (strstr
>>>>>>> + (cpu_flags, "AVX512")
>>>>>>> +      && !strstr (cpu_flags, "AVX512PF")
>>>>>>> +      && !strstr (cpu_flags, "AVX512ER")
>>>>>>> +      && !strstr (cpu_flags, "4FMAPS")
>>>>>>> +      && !strstr (cpu_flags, "4VNNIW")
>>>>>>> +      && !strstr (cpu_flags, "VP2INTERSECT"))
>>>>>>> +    {
>>>>>>> +      cpu_flags = concat (cpu_flags, "|AVX10_1", NULL);
>>>>>>> +      k = 1;
>>>>>>> +    }
>>>>>>>    free (ident);
>>>>>>
>>>>>> While making a patch myself along the lines of what I had outlined,
>>>>>> I came to realize that the above isn't enough. (I'm pretty sure I
>>>>>> wouldn't have spotted this by merely reviewing your patch.) This
>>>>>> may be a result of the spec being somewhat ambiguous when it comes
>>>>>> to GFNI,
>>>> VAES, and VPCLMULQDQ.
>>>>>> There's a note there saying something about the respective EVEX
>>>> encodings.
>>>>>> But that still requires the VEX encodings connected to these three
>>>>>> features to also become suitably available. While this works fine
>>>>>> for GFNI, it doesn't for the other two: The 128-bit VEX encodings,
>>>>>> which surely are available when the 256-bit ones are, would become
>>>>>> impossible to use. The assembler would pick the (larger) EVEX forms
>>>>>> instead. There are two ways to solve this that I can see right away:
>>>>>> 1) AES becomes a dependency of VAES (and PCLMULQDQ one of
>>>>>> VPCLMULQDQ)
>>>>>> 2) We put in place extra templates.
>>>>>> I'm wary of the first option as long as not at least informally
>>>>>> supported by you (Intel). Hence I went with option 2 for now.
>>>>>>
>>>>>> I'm only done with the /512 patch, so I won't post right away. I'm
>>>>>> still debating with myself whether to control maximum vector length
>>>>>> via a new directive, or via a special form of .arch.
>>>>>
>>>>> Do you think a command line option like -mavx10maxvl=256/512 with
>>>>> default 512 is ok for this scenario? I am working to revise the
>>>>> AVX10.1 patch
>>>> like that.
>>>>
>>>> That's certainly an option, but right now I have different plans.
>>>
>>> Actually all the three options are ok for me, they should not be that
>>> complex based on the current part of v3 patch setting/clearing AVX512 bit
>> for AVX10.1.
>>
>> Mind me asking what "all the three options" you're referring to here?
> 
> A new directive, a special form of .arch or the command line option.

Oh, I see. Whatever we choose, it'll need to come in both command line
and directive form, I think. And then both want to be sufficiently
similar. As mentioned, I have a firm plan now, but of course I need to
see whether it ends up looking sensibly once actually carried out.

Jan