Re: [Ping] [PATCH 0/4] Add AMX support.

[Luis Machado <luis.machado@arm.com>]

On 5/25/22 10:14, Willgerodt, Felix via Gdb-patches wrote:
>> -----Original Message-----
>> From: John Baldwin <jhb@FreeBSD.org>
>> Sent: Freitag, 20. Mai 2022 18:29
>> To: Willgerodt, Felix <felix.willgerodt@intel.com>; gdb-
>> patches@sourceware.org
>> Subject: Re: [Ping] [PATCH 0/4] Add AMX support.
>>
>> On 5/20/22 7:40 AM, Willgerodt, Felix via Gdb-patches wrote:
>>> *Ping*
>>>
>>> I have adapted all of Eli's comments on documentation locally.
>>> They were all straightforward, so I didn't post a v2 for those yet.
>>
>> I don't have any further feedback.  I will say that I think it's fine to not
>> support dynamic tile sizes.  I think the aarch64 arch in GDB uses the same
>> approach with respect to SVE which is to say that the SVE vector size
>> is fixed for a given process' lifetime (or something along those lines).
>>
> 
> I couldn't try SVE myself, but it seems like SVE is actually updated at each
> BP, at least for native Linux GDB targets,
> see aarch64_linux_nat_target::thread_architecture().
> 
> We tried implementing it that way as well, but the gdbserver
> infrastructure to handle target description updates doesn't really exist.

That is the main barrier for supporting vector/matrix length updates mid-execution for remote targets.

There was some early discussions here: https://sourceware.org/pipermail/gdb/2020-January/048274.html

But there wasn't much consensus on the best way to do it.

Ideally we'd have a proper sizeless type to describe the scalable vector/matrix, based on a dynamic
property (a register, for example). But that requires many more changes.

> 
> That said, I don't think a fixed AMX dimension would provide a good
> user experience though. Neither in the case of showing the whole
> register nor when using a fixed dimension for a process' lifetime.> 
> Regards,
> Felix
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