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bc6d6a4172
Add an implementation of sha256_finup_2x_arch() for x86_64. It
interleaves the computation of two SHA-256 hashes using the x86 SHA-NI
instructions. dm-verity and fs-verity will take advantage of this for
greatly improved performance on capable CPUs.
This increases the throughput of SHA-256 hashing 4096-byte messages by
the following amounts on the following CPUs:
Intel Ice Lake (server): 4%
Intel Sapphire Rapids: 38%
Intel Emerald Rapids: 38%
AMD Zen 1 (Threadripper 1950X): 84%
AMD Zen 4 (EPYC 9B14): 98%
AMD Zen 5 (Ryzen 9 9950X): 64%
For now, this seems to benefit AMD more than Intel. This seems to be
because current AMD CPUs support concurrent execution of the SHA-NI
instructions, but unfortunately current Intel CPUs don't, except for the
sha256msg2 instruction. Hopefully future Intel CPUs will support SHA-NI
on more execution ports. Zen 1 supports 2 concurrent sha256rnds2, and
Zen 4 supports 4 concurrent sha256rnds2, which suggests that even better
performance may be achievable on Zen 4 by interleaving more than two
hashes. However, doing so poses a number of trade-offs, and furthermore
Zen 5 goes back to supporting "only" 2 concurrent sha256rnds2.
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20250915160819.140019-4-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.