On 4/4/24 16:36, Eric Biggers wrote: > 1. Never use zmm registers. ... > 4. Keep the proposed policy as the default behavior, but allow it to be > overridden on the kernel command line. This would be a bit more flexible; > however, most people don't change defaults anyway. > > When you write "Some folks will also surely disagree with the kernel policy > implemented here", are there any specific concerns that you anticipate? Some people care less about the frequency throttling and only care about max performance _using_ AVX512. > Note that Intel has acknowledged the zmm downclocking issues on Ice > Lake and suggested that using ymm registers instead would be > reasonable:> https://lore.kernel.org/linux-crypto/e8ce1146-3952-6977-1d0e-a22758e58914@xxxxxxxxx/ > > If there is really a controversy, my vote is that for now we just go with option > (1), i.e. drop this patch from the series. We can reconsider the issue when a > CPU is released with better 512-bit support. (1) is fine with me. (4) would also be fine. But I don't think it absolutely _has_ to be a boot-time switch. What prevents you from registering, say, "xts-aes-vaes-avx10" and then doing: if (avx512_is_desired()) xts-aes-vaes-avx10_512(...); else xts-aes-vaes-avx10_256(...); at runtime? Where avx512_is_desired() can be changed willy-nilly, either with a command-line parameter or runtime knob. Sure, the performance might change versus what was measured, but I don't think that's a deal breaker. Then if folks want to do fancy benchmarks or model/family checks or whatever, they can do it in userspace at runtime.
