Google engineer Eric Biggers continues making very significant performance optimizations to the Linux kernel crypto code. One of his latest focuses has been on enhancing dm-verity performance by using two-way interleaved SHA-256 hashing for data blocks.
Biggers explained with the commit achieving this performance breakthrough:
"When the crypto library provides an optimized implementation of sha256_finup_2x(), use it to interleave the hashing of pairs of data blocks. On some CPUs this nearly doubles hashing performance. The increase in overall throughput of cold-cache dm-verity reads that I'm seeing on arm64 and x86_64 is roughly 35% (though this metric is hard to measure as it jumps around a lot).
For now this is done only on data blocks, not Merkle tree blocks. We could use sha256_finup_2x() on Merkle tree blocks too, but that is less important as there aren't as many Merkle tree blocks as data blocks, and that would require some additional code restructuring."
A significant win for those relying on DM-VERITY integrity protections. This two-way interleaved SHA-256 hashing for DM-VERITY is queued into Device-Mapper's "for-next" Git branch and thus is expected to become part of the Linux 6.19 kernel in the coming months.