Re: bizarre network timing problem

[Rick Jones]

Felix von Leitner wrote:
> Thus spake Rick Jones (rick.jones2@xxxxxx):
>
> > 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.

rick jones
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