cleanup the RAID6 P/Q library v3

[Christoph Hellwig]

On Fri, Jun 26, 2026 at 05:52:18PM -0700, H. Peter Anvin wrote:
> On 2026-05-19 01:24, Christoph Hellwig wrote:
> > 
> > raid6: rework registration of optimized algorithms
> > 
> >  - avx2 instead of avx512 is probably the right thing for no
> >    benchmarking, but if it was intentional (it wasn't), that should
> >    be document.  So I'll just switch back to the previous version to
> >    keep the state of the art
> 
> It is unlikely to be the right thing *going forward*, though.
> 
> The very unfortunate performance inversion is likely model-specific. It is one
> of those things where you largely would have to have a list of quirks :(

Note that the default is still to benchmark the implementations.
This is just about the case where the user explicitly disabled that
benchmark-based selection.