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Date: Tue, 06 Nov 2007 13:12:13 -0800 From: Rick Jones <rick.jones2@...com> To: Felix von Leitner <felix-linuxkernel@...e.de> Cc: Chuck Ebbert <cebbert@...hat.com>, linux-kernel@...r.kernel.org, Netdev <netdev@...r.kernel.org> Subject: Re: bizarre network timing problem Felix von Leitner wrote: > Thus spake Rick Jones (rick.jones2@...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. rick jones - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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