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The P/Q left side optimization in the delta syndrome simply involves repeatedly multiplying a value by polynomial 'x' in GF(2^8). Given that 'x * x * x * x' equals 'x^4' even in the polynomial world, we can accelerate this substantially by performing up to 4 such operations at once, using the NEON instructions for polynomial multiplication. Results on a Cortex-A57 running in 64-bit mode: Before: ------- raid6: neonx1 xor() 1680 MB/s raid6: neonx2 xor() 2286 MB/s raid6: neonx4 xor() 3162 MB/s raid6: neonx8 xor() 3389 MB/s After: ------ raid6: neonx1 xor() 2281 MB/s raid6: neonx2 xor() 3362 MB/s raid6: neonx4 xor() 3787 MB/s raid6: neonx8 xor() 4239 MB/s While we're at it, simplify MASK() by using a signed shift rather than a vector compare involving a temp register. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.