Here are more benchmarks of vanilla 3.4 vs. cityhash vs. fast_hash_3 on both arm7l and x86-64. The patch was applied varbatim, only caching disabled. On arm7l, the cpu was fixed to maximum freq (it seems to take ages to switch frequencies, at least there is a lot of jitter with ondemand). The cityhash implementation was compiled with -O3 on both platforms and -msse4.2 on x86-64.

CityHash and fh3 come out much better than vanilla on x86-64 with cityhash being slightly faster (which is surprising). On ARM7 CityHash performs much worse than vanilla and fh3 significantly better.