Re:Homebrew: AVX instructions in Big Sur bottles crash when ...
by phire on Saturday December 26, 2020 @09:16PM
(#25548245)
No. For many algorithms, AVX isn't a 2x speedup over SSE. Especially when lanes are conditionally masked.
Often you are happy to get a 1.25x speed up with AVX. Sometimes it actually goes slower.
If you were to emulate that code with a 1.25x speedup with AVX on the M1, you would end up with all the disadvantages of going to 8-wide, but with none of the speedup.
That 1.25x speedup is halved and the emulated AVX code actually runs at about 0.625x the speed of the emulated SSE code path.
Often you are happy to get a 1.25x speed up with AVX. Sometimes it actually goes slower.
If you were to emulate that code with a 1.25x speedup with AVX on the M1, you would end up with all the disadvantages of going to 8-wide, but with none of the speedup.
That 1.25x speedup is halved and the emulated AVX code actually runs at about 0.625x the speed of the emulated SSE code path.