perf report shows this function “__memset_avx2_unaligned_erms” has overhead. does this mean memory is unaligned?

The name of the pictureThe name of the pictureThe name of the pictureClash Royale CLAN TAG#URR8PPP


perf report shows this function “__memset_avx2_unaligned_erms” has overhead. does this mean memory is unaligned?



I am trying to profile my C++ code using perf tool. Implementation contains code with SSE/AVX/AVX2 instructions. In addition to that code is compiled with -O3 -mavx2 -march=native flags. I believe __memset_avx2_unaligned_erms function is a libc implementation of memset. perf shows that this function has considerable overhead. Function name indicates that memory is unaligned, however in the code I am explicitly aligning the memory using GCC built-in macro __attribute__((aligned (x))) What might be the reason for this function to have significant overhead and also why unaligned version is called although memory is aligned explicitly?


-O3 -mavx2 -march=native


__memset_avx2_unaligned_erms


memset


__attribute__((aligned (x)))



I have attached the sample report as picture.enter image description here





memset happens to be implemented in a way that does not require alignment.
– Marc Glisse
56 secs ago









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