Messages in this thread | | | Date | Tue, 06 Nov 2007 13:12:13 -0800 | From | Rick Jones <> | Subject | Re: bizarre network timing problem |
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Felix von Leitner wrote: > Thus spake Rick Jones (rick.jones2@hp.com): > >>Past performance is no guarantee of current correctness :) And over an >>Ethernet, there will be a very different set of both timings and TCP >>segment sizes compared to loopback. > >>My guess is that you will find setting the lo mtu to 1500 a very >>interesting experiment. > > Setting the MTU on lo to 1500 eliminates the problem and gives me double > digit MB/sec throughput.
I'm not in a position at the moment to test it as my IPoIB systems are offline, and not sure you are either, but I will note that with IPoIB bits circa OFED1.2 the default MTU for IPoIB goes up to 65520 bytes. If indeed the problem you were seeing was related to sub-mss sends and window probing and such, it might appear on IPoIB in addition to loopback.
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