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The CRC-T10DIF implementation for arm64 has a version that uses 8x8 polynomial multiplication, for cores that lack the crypto extensions, which cover the 64x64 polynomial multiplication instruction that the algorithm was built around. This fallback version rather naively adopted the 64x64 polynomial multiplication algorithm that I ported from ARM for the GHASH driver, which needs 8 PMULL8 instructions to implement one PMULL64. This is reasonable, given that each 8-bit vector element needs to be multiplied with each element in the other vector, producing 8 vectors with partial results that need to be combined to yield the correct result. However, most PMULL64 invocations in the CRC-T10DIF code involve multiplication by a pair of 16-bit folding coefficients, and so all the partial results from higher order bytes will be zero, and there is no need to calculate them to begin with. Then, the CRC-T10DIF algorithm always XORs the output values of the PMULL64 instructions being issued in pairs, and so there is no need to faithfully implement each individual PMULL64 instruction, as long as XORing the results pairwise produces the expected result. Implementing these improvements results in a speedup of 3.3x on low-end platforms such as Raspberry Pi 4 (Cortex-A72) Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> |
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.