Eric Biggers who has been known for his relentless crypto kernel optimizations over the years sent out a new patch series on Wednesday to better clean-up the ChaCha and BLAKE2s code. As part of that patch series is also enabling the architecture-optimized BLAKE2s code by default, similar to the process other crypto algorithms have gone through.
Of the patch series most interesting is the patch to always enable the arch-optimized BLAKE2s code. There he argues:
"When support for a crypto algorithm is enabled, the arch-optimized implementation of that algorithm should be enabled too. We've learned this the hard way many times over the years: people regularly forget to enable the arch-optimized implementations of the crypto algorithms, resulting in significant performance being left on the table.
Currently, BLAKE2s support is always enabled ('obj-y'), since random.c uses it. Therefore, the arch-optimized BLAKE2s code, which exists for ARM and x86_64, should be always enabled too. Let's do that.
Note that the effect on kernel image size is very small and should not be a concern. On ARM, enabling CRYPTO_BLAKE2S_ARM actually *shrinks* the kernel size by about 1200 bytes, since the ARM-optimized blake2s_compress() completely replaces the generic blake2s_compress(). On x86_64, enabling CRYPTO_BLAKE2S_X86 increases the kernel size by about 1400 bytes, as the generic blake2s_compress() is still included as a fallback; however, for context, that is only about a quarter the size of the generic blake2s_compress(). The x86_64 optimized BLAKE2s code uses much less icache at runtime than the generic code."
In the case of the x86_64 optimized BLAKE2s, this allows for SSSE3 and AVX-512 usage for faster BLAKE2s cryptographic hashing performance.