Hi Eric, I computed performance numbers for both 32-bit and 64-bit using the actual functions in which talking about replacing MD5 with SipHash. The basic harness is here [1] if you're curious. SipHash was a pretty clear winner for both cases.
x86_64: [ 1.714302] secure_tcpv6_sequence_number_md5# cycles: 102373398 [ 1.747685] secure_tcp_sequence_number_md5# cycles: 92042258 [ 1.773522] secure_tcpv6_sequence_number_siphash# cycles: 70786533 [ 1.798701] secure_tcp_sequence_number_siphash# cycles: 68941043 x86: [ 1.635749] secure_tcpv6_sequence_number_md5# cycles: 106016335 [ 1.670259] secure_tcp_sequence_number_md5# cycles: 95670512 [ 1.708387] secure_tcpv6_sequence_number_siphash# cycles: 105988635 [ 1.740264] secure_tcp_sequence_number_siphash# cycles: 88225395 >>> 102373398 > 70786533 True >>> 92042258 > 68941043 True >>> 106016335 > 105988635 True >>> 95670512 > 88225395 True While MD5 is probably faster for some kind of large-data cycles-per-byte, due to its 64-byte internal state, SipHash -- the "Sip" part standing "Short Input PRF" -- is fast for shorter inputs. In practice with the functions we're talking about replacing, there's no need to hash 64-bytes. So, SipHash comes out faster and more secure. I also haven't begun to look focusedly at the assembly my SipHash implemention is generating, which means there's still window for even more performance improvements. Jason [1] https://git.zx2c4.com/linux-dev/tree/net/core/secure_seq.c?h=siphash-bench#n194
