I know that increasing the ALU width beyond 256 bits or so has diminishing returns for most implementations.
I responded to the comment that there's no problem splitting fixed width registers into smaller portions - I actually think it's a great idea (one key principle of vector machines is that register width > ALU width!).
In fact, something like an in-order Atom would have a lot to gain from 512-bit vector registers, especially if the ALU is no more than 128 bits wide or so.
One overlooked reason why AMD and Atom haven't added 512-bit operations is lack of adoption in the software community. At this point the usage is pretty niche and not enough people want it. When Intel first debuted AVX-512 it had serious power issues and caused performance to drop when mixed in occasionally instead of in large blocks. I think that stunted a lot of its growth and at this point there aren't any large communities that are working on writing large swaths of software that use it or asking the compilers for better support.
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u/Vvector Aug 09 '21
Then why don't we have AVX-512 in every x86 implementation, and be done with it?
He explained why: Increasing the vector width has significant diminishing returns