> From: Konstantin Ananyev [mailto:[email protected]] > Sent: Wednesday, 5 August 2026 07.46 > > > > From: Stephen Hemminger [mailto:[email protected]] > > > Sent: Tuesday, 4 August 2026 17.52 > > > > > > On Tue, 4 Aug 2026 14:33:04 +0000 > > > Morten Brørup <[email protected]> wrote: > > > > > > > + /* Common way for small copy size of 64-byte blocks. > Unlikely, so > > > constant size only */ > > > > + if (__rte_constant(n) && (n & 63) == 0 && n <= > > > RTE_MEMCPY_BLOCK_64_MAX) { > > > > + void *ret = dst; > > > > + > > > > > > Maybe just let compiler decide, it will generate vector > instructions in > > > most cases. > > > > > > if (__rte_constant(n)) > > > return mempcpy(dst, src, n); > > > > Maybe in most, but not in all: > > https://godbolt.org/z/KvdKqT5rY > > With '-mavx' or '-mavx512f' it looks like it does for your sample code.
It also does with -msse4.2 when SZ is reduced to 256 bytes. Clang switches to inline when SZ is reduced to 128 bytes. It seems the compiler has a threshold for when to inline and when to call the C library's memcpy subroutine. The threshold depends on both copy size and vector register size. And it is compiler dependent. With rte_memcpy() it is always inline.
