riscv: optimise memcpy when misalign #71
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…s. It will first align destination pointer to word-boundary regardless whether src and dest are co-aligned or not. If they indeed are, then wordwise copy is performed. If they are not co-aligned, then it will load two adjacent words from src and use shifts to assemble a full machine word.
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How to test? memcpy.S link: https://github.com/revyos/thead-kernel/blob/lpi4a/arch/riscv/lib/memcpy.S memcpy.c header file mkdir memcpy_test cd memcpy_test original memcpy.S modifyed memcpy.S |
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riscv: __asm_copy_to-from_user: Optimize unaligned memory access |
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Why not keep the original commit message? |
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The current behaviour of memcpy is that it checks if both src and dest pointers are co-aligned . If aligned, it will copy data word-by-word after first aligning pointers to word boundary. If src and dst are not co-aligned, however, byte-wise copy will be performed.
This patch optimises memcpy for misaligned cases. It will first align destination pointer to word-boundary regardless whether src and dest are co-aligned or not. If they indeed are, then wordwise copy is performed. If they are not co-aligned, then it will load two adjacent words from src and use shifts to assemble a full machine word.
In my testing this speeds up memcpy 4~5x when src and dest are not co-aligned.