On Tuesday 20 February 2007 11:12, David Miller wrote: > From: Eric Dumazet <[EMAIL PROTECTED]> > Date: Tue, 20 Feb 2007 11:04:15 +0100 > > > Using a jenkin's hash permits a better hash distribution for a litle > > cpu cost. I will post later a distribution simulation based on the > > data gathered from the same real server. > > Actually someone (I think it was Evgeniy in fact) made such > comparisons and found in his studies that not only does the current > ehash xor hash function distribute about as well as jenkins, it's > significantly cheaper to calculate :-) > > If you find jenkins is better, great, but I hope it works that > way for many workloads.
Here are results from real workload : ehash_addr=0xffff810476000000 ehash_size=1048576 330241 chains, 2441 twchains Distribution of sockets/chain length [chain length]:number of sockets [0]:718335 0% [1]:223485 42.1436% [2]:60655 65.0196% [3]:22451 77.7207% [4]:11164 86.1416% [5]:6376 92.1534% [6]:3236 95.8148% [7]:1600 97.9268% [8]:793 99.1231% [9]:286 99.6085% [10]:111 99.8178% [11]:56 99.934% [12]:20 99.9793% [13]:4 99.9891% [14]:2 99.9943% [15]:2 100% total : 530294 sockets Imagine we double hash size (2097152). Distribution would be: [0]:1698209 0% [1]:309255 58.3177% [2]:61638 81.5644% [3]:18593 92.0829% [4]:6479 96.97% [5]:2092 98.9425% [6]:655 99.6836% [7]:184 99.9265% [8]:37 99.9823% [9]:6 99.9925% [10]:4 100% If we use jenkin hash: jhash_3words(daddr, saddr, (dport<<16)|sport, 0); [0]:632435 0% [1]:319916 60.328% [2]:80465 90.6754% [3]:13816 98.4914% [4]:1735 99.8001% [5]:196 99.9849% [6]:11 99.9974% [7]:2 100% - 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
