Did you set io.file.buffer.size (or whatever the property is) to a large value? If you didn't, then hadoop will explicitly create packets at the default size, and you'll see zero utilization of the jumboframes. (although that would argue for a flat performance, no? do jumbo frames have increased overhead-per-packet that could come into play with smaller packets here?)
Also, even if you do set that, I'm not 100% sure that it will lead to use of the jumboframes, I'd have to take a look through the code to be sure. Another issue is that you may lose any networking performance gains as a result of increased buffer allocation costs and garbage collection. Ed, I threw out the radfs experiment, I'm working on HDFS-918 now -- that's what I was mentioning the other night as being possibly more conducive to jumbo frames due to less buffer allocation on BlockSender instantiation. But I haven't benchmarked yet so that's all very much "in theory" On Tue, Jan 26, 2010 at 1:12 PM, stephen mulcahy <[email protected]>wrote: > Eli Collins wrote: > >> I was somewhat surprised at the results of enabling Jumbo frames - it >>> resulted in a slowdown. In the case of the write operations, the slow >>> down >>> was about 5%. In the case of 10GB sort, the slowdown was around 6% and in >>> the case of the 100GB sort, the slowdown was nearly 20%. >>> >> >> Are normal (non-hadoop) file transfers faster between the same hosts >> with jumbo frames enabled? ie have your ruled out host/configuration >> issues? >> > > Yes - I did some testing on two different clusters we have - both with and > without jumbo frames and in both cases, I saw a small but noticeable > increase in the overall bandwidth when moving from an MTU of 1500 to an MTU > of 9000. > > Has anyone else tested Hadoop performance with Jumbo frames? Are you seeing > something different to what we're seeing? > > Thanks, > > -stephen > > > -- > Stephen Mulcahy, DI2, Digital Enterprise Research Institute, > NUI Galway, IDA Business Park, Lower Dangan, Galway, Ireland > http://di2.deri.ie http://webstar.deri.ie http://sindice.com >
