On all RISC-V CPUs I have currently access to with the pre-ratification RVV 0.7.1, the simple 9 instruction memcpy function shown by camel-cdr is faster than any other kind of memcpy (simple byte-by-byte loop with no decision overhead, or complex glibc function) at EVERY sensible size.

These range from the C906 core found in Linux-capable boards costing $6 or $10 (Pine64 Ox64, Sipeed M1s, Milk-V Duo), the the C920 OoO cores in the 64 core SOPHON SG2042.

Here are some numbers I ran on a 1 GHz C906 over two years ago:

https://hoult.org/d1_memcpy.txt

The short RVV function has absolutely constant execution time out to n=64 AND this time is 40% less than standard memcpy even at size 0 or 1 byte, and from 8 to 128 bytes it is at least 3x faster.

A 1.8x advantage is maintained for any size that fits in L1 cache, then after that both are able to saturate the memory bus.

Remember, this is a low-end in-order core (similar to Cortex-A35) designed in 2019, with only 128 bit vector registers and ALU. But the same thing applies on newer, higher-performance cores.