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836ed3c4e4
Make memcpy(), memmove() and memset() use the Armv8.8 FEAT_MOPS instructions when implemented on the CPU. The CPY*/SET* instructions copy or set a block of memory of arbitrary size and alignment. They can be interrupted by the CPU and the copying resumed later. Their performance is expected to be close to the best generic copy/set sequence of loads/stores for a given CPU. Using them in the kernel's copy/set routines therefore avoids the need to periodically rewrite the routines to optimize for new microarchitectures. It could also lead to a performance improvement for some CPUs and systems. With this change the kernel will always use the instructions if they are implemented on the CPU (and have not been disabled by the arm64.nomops command line parameter). When not implemented the usual routines will be used (patched via alternatives). Note, we need to patch B/NOP instead of the whole sequence to avoid executing a partially patched sequence in case the compiler generates a mem*() call inside the alternatives patching code. Note that MOPS instructions have relaxed behavior on Device memory, but it is expected that these routines are not generally used on MMIO. Note: For memcpy(), this uses the CPY* instructions instead of CPYF*, as CPY* allows overlaps between the source and destination buffers, and despite contradicting the C standard, compilers require that memcpy() work on exactly overlapping source and destination: https://gcc.gnu.org/onlinedocs/gcc/Standards.html#C-Language https://reviews.llvm.org/D86993 Signed-off-by: Kristina Martsenko <kristina.martsenko@arm.com> Link: https://lore.kernel.org/r/20240930161051.3777828-5-kristina.martsenko@arm.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> |
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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.