Benchmarks: align malloc'ed buffers.#3794
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martin-frbg merged 2 commits intoOpenMathLib:developfrom Oct 21, 2022
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Benchmarks should allocate with cacheline (often 64 bytes) alignment to avoid unreliable timings. This technique, storing the offset in the byte before the pointer, doesn't require C11's aligned_alloc for compatibility with older compilers. For example, Glibc's x86_64 malloc returns 16-byte aligned buffers, which is not sufficient for AVX/AVX2 (32-byte preferred) or AVX512 (64-byte).
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It stores the pointer, not an offset (that would be an alternative approach).
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Benchmarks should allocate with cacheline (often 64 bytes) alignment to avoid unreliable timings. This technique, storing the offset in the byte before the pointer, doesn't require C11's aligned_alloc for compatibility with older compilers.
For example, Glibc's x86_64 malloc returns 16-byte aligned buffers, which is not sufficient for AVX/AVX2 (32-byte preferred) or AVX512 (64-byte).