Hi Jason, On Tue, Oct 31, 2017 at 12:57:29PM +0100, Jason A. Donenfeld wrote: > On Tue, Oct 31, 2017 at 12:51 PM, Will Deacon <will.dea...@arm.com> wrote: > > Which code in the kernel actually uses 128-bit types directly? I know we > > have some unfortunate occurences in our headers (including uapi) for the > > vector registers, but I thought we generally used asm or copy routines to > > access those. > > math64.h provides it, and various things throughout use those > functions. Notably, the scheduler and kvm use those the __int128 > functions. There's also an elliptic curve implementation that uses it, > which makes a big difference. And soon I'll be adding an > implementation of curve25519 that will make heavy use of these > instructions for significant speedups as well.
Thanks for the info. It does indeed look like mul_u64_u64_shr improves pretty drastically with this patch, so that sounds good to me. We don't ever call that function on arm64, but hey. > Generally, adding this CONFIG_ARCH key is a hint for current and > future bits of code, so that they can use the faster 128-bit > implementations when available. Not providing it when it's there and > available would be silly. This wasn't originally added to the > architecture, because when the Kconfig symbol was added, gcc didn't > have sane support for it on aarch64. But now it does, so let's support > it. Sure, I'll wait for your patch that matches the relevant compiler versions. Will