On Thu, Aug 29, 2013 at 1:27 AM, T.C. Gubatayao <tgubata...@barracuda.com>wrote:
> > No problem with fnv_hash(). > > Doesn't it have bad mixing? Good distribution is important since this > code is > for load balancing. > The poor mixing in FNV hash comes from the 8-bit XOR operation. But that provides fine mixing of the last 8 bits, which should be sufficient for lagg_hash unless people are lagging together > 256 ports. > > FNV is also slower compared to most of the newer non-cryptographic hashes, > certainly on large keys, but even on small ones. Of course, performance > will > vary with the architecture. > > > While I agree that it is likely that siphash24() is slower if you could > afford > > the time do a test run it would be great to from guess to know. > > +1 > You might want to consider lookup3 too, since it's also readily available > in the > kernel [1]. > I pulled all four hash functions out into userland and microbenchmarked them. The upshot is that hash32 and fnv_hash are the fastest, jenkins_hash is slower, and siphash24 is the slowest. Also, Clang resulted in much faster code than gcc. http://people.freebsd.org/~asomers/lagg_hash/ [root@sm4u-4 /usr/home/alans/ctest/lagg_hash]# ./lagg_hash-gcc-4.8 FNV: 0.76 hash32: 1.18 SipHash24: 44.39 Jenkins: 6.20 [root@sm4u-4 /usr/home/alans/ctest/lagg_hash]# ./lagg_hash-gcc-4.2.1 FNV: 0.74 hash32: 1.35 SipHash24: 55.25 Jenkins: 7.37 [root@sm4u-4 /usr/home/alans/ctest/lagg_hash]# ./lagg_hash.clang-3.3 FNV: 0.30 hash32: 0.30 SipHash24: 55.97 Jenkins: 6.45 [root@sm4u-4 /usr/home/alans/ctest/lagg_hash]# ./lagg_hash.clang-3.2 FNV: 0.30 hash32: 0.30 SipHash24: 44.52 Jenkins: 6.48 > T.C. > > [1] > http://svnweb.freebsd.org/base/head/sys/libkern/jenkins_hash.c?view=markup _______________________________________________ freebsd-net@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"