On Sun, Jun 2, 2019 at 7:21 AM Michal Suchánek <msuchanek@xxxxxxx> wrote: > > Hello, > > On Sun, 2 Jun 2019 06:43:07 -0400 > Jeffrey Walton <noloader@xxxxxxxxx> wrote: > > > Hi Everyone, > > > > I have a lot of experience with cutting in SHA acceleration. I have no > > experience with Git. > > sha1 is dead. Git is planning to move away from it. It will not happen > overnight but it probably does not make sense to accelerate it at this > point. > > https://github.com/git/git/blob/next/Documentation/technical/hash-function-transition.txt SHA-1 has been dead for years. That has not stopped Git yet :) My guess is, Git will have to carry around a SHA-1 implementation for a decade or so for interop purposes. > > If someone would setup a fork and provide a call like: > > > > // https://github.com/torvalds/linux/blob/master/arch/x86/include/asm/cpufeature.h > > // Or whatever the project prefers > > has_x86_sha = cpu_feature_enabled(X86_FEATURE_SHA_NI); > > > > if (has_x86_sha) > > { > > sha1_hash_block(state, ptr, size); > > } > > > > And provide a stub: > > > > sha1_hash_block(uint32_t* state, uint8_t* ptr, size_t size) > > { > > } > > > > Then I would be happy to fill in the pieces. > > > > I can also help with ARMv8. > > > > In fact, if you want to use Andy Polyakov's asm from Cryptogams > > (https://www.openssl.org/~appro/cryptogams/), then I can help with > > that, too. Andy's skills are renowned and his code is used in the > > kernel. > > And buggy. I am not referring to the sha1 implementation in particular > but to the hand-crafted assembly in general. > > Do you have some performance data that shows significant improvement of > common tasks that makes maintaining this hackery worthwhile? Well, considering Git carries along an SHA-1 implementation with undefined behavior, anything would be an improvement since it can't pass acceptance testing out of the box. And Git does that for a 0.01 to 0.03 cpb increase in spperformance. For SHA-1 intrinsics on x86, performance increases to about 1.7 cpb. For SHA-256 performance increases to 3.8 cpb. On ARMv8, performance will increase to about 2.0 cpb on A-53 cpu's, and about 1.5 to 1.0 cpb on A-57 cpus. Comparing against a standard C/C++ implementation, Git will see a 3x to 6x speedup depending on the platform and algorithm. Jeff
