On Sat, Sep 1, 2018 at 1:19 PM, Jason A. Donenfeld <Jason@xxxxxxxxx> wrote: > Hey Thomas, > > I'd like to move ahead with my patchset and make some forward progress > in LKML submission. If you've got something brewing regarding the FPU > context on x86 and ARM, I'm happy to wait a bit longer so as to build > on that. But if that is instead a far-off theoretical eventual thing, > perhaps it's better for me to move ahead as planned, and we can switch > to the superior FPU semantics whenever you get around to it? Either > way, please let me know what you have in mind so our plans can stay > somewhat sync'd. I tend to think the right approach is to merge Jason's code and then make it better later. Even with a totally perfect lazy FPU restore implementation on x86, we'll probably still need some way of dealing with SIMD contexts. I think we're highly unlikely to ever a allow SIMD usage in all NMI contexts, for example, and there will always be cases where we specifically don't want to use all available SIMD capabilities even if we can. For example, generating random numbers does crypto, but we probably don't want to do *SIMD* crypto, since that will force a save and restore and will probably fire up the AVX512 unit, and that's not worth it unless we're already using it for some other reason. Also, as Rik has discovered, lazy FPU restore is conceptually straightforward but isn't entirely trivial :) --Andy
