From: "Brian F. G. Bidulock" <[EMAIL PROTECTED]> Date: Wed, 31 May 2006 02:49:54 -0600
> This would be faster than a Jenkins hash approach because it > would not be necessary to calculate the hash function at all for > in-window segments. Per packet overheads would decrease and > better small packet performance would be experienced (i.e. your > http server). It has better hash coverage because MD4 and other > cryptographic algorithms used for initial sequence number > selection have far better properties than Jenkins. > > What do you think? I don't know how practical this is. The 4GB sequence space wraps very fast on 10 gigabit, so we'd be rehashing a bit and 100 gigabit would make things worse whenever that shows up. It is, however, definitely an interesting idea. We also need the pure traditional hashes for net channels. I don't see how we could use your scheme for net channels, because we are just hashing in the interrupt handler of the network device driver in order to get a queue to tack the packet onto, we're not interpreting the sequence numbers and thus would not able to maintain the sequence space based hashing state. On a 3ghz cpu, the jenkins hash is essentially free. Even on slower cpus, jhash_2words for example is just 20 cycles on a sparc64 chip. It's ~40 integer instructions and they all pair up perfectly to dual issue. We'd probably use jhash_3words() for TCP ipv4 which would get us into the 30 cycle range. A few years ago when I introduced jenkins into the tree, I thought it's execution cost might be an issue. I really don't anymore. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
