On Sat, Nov 21, 2020 at 10:57 AM Jeffrey Walton noloader@gmail.com wrote:
On Sat, Nov 21, 2020 at 10:20 AM David Edelsohn dje.gcc@gmail.com wrote:
Please don't target Power7. Please target Power9, or at least Power8.
The PPC64LE Linux ABI specifies Power8 as the minimum ISA.
Power ISA 2.07 is Power8. ISA 3.0 is Power9. ISA 3.1 is Power10.
Small nit... PowerMac G4's and G5's still have a strong following. There's a lot of activity on Debian's PowerPC list.
The G4's and G5's provide Altivec acceleration and the old gcc compiler even accepts -mcpu=power4.
ChaCha is a simple algorithm that benefits from Altivec, even when you manage the 64-bit additions/carries in a 32x4 vector arrangement.
Small nit: G4 and G5 Macs are not Power7. If an implementation of a cipher targets Power7, it still can use ISA instructions not supported by PowerMacs. If you want to provide an additional implementation for pure Altivec, that's fine.
There is a vocal group of Debian PowerPC users. I greatly appreciate support and advocacy. But the number of actual users is very small. And it's highly unlikely that those users will run ChaCha cipher in production. The ChaCha implementation is new, not maintaining existing support.
If Niels wants to implement an optimized version of a cipher on Power that will be useful in production environments and applied in global businesses, I would recommend that he target Power9. A new, high-performance implementation will be deployed on new systems for new applications or new versions of applications.
Thanks, David