[ofa-general] [Bug 450] IPoIB BW drop (measured with iperf) with mtu=1500 on x86 RH4UP3

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https://bugs.openfabrics.org/show_bug.cgi?id=450





------- Comment #6 from mst at dev.mellanox.co.il  2007-03-14 02:54 -------
Subject: Re: [ofa-general]  New: IPoIB BW drop (measured with iperf)
        with mtu=1500 on x86 RH4UP3

> Quoting Moni Levy <monil at voltaire.com>:
> Subject: Re: [ofa-general] [Bug 450] New: IPoIB BW drop (measured with iperf) with mtu=1500 on x86 RH4UP3
> 
> On 3/13/07, Michael S. Tsirkin <mst at dev.mellanox.co.il> wrote:
> >> >Why are you playing with ifc mtu?
> >>
> >> We needed to do some IP forwarding tests between IB and Ethernet and
> >> wanted to have the same MTU for the eth0 and ib0 interfaces, after
> >> that we reproduced that in a peer to peer configuration.
> >
> >OK but PMTU discovery would do this better, won't it?
> 
> I'm not sure (it will probably drop some packets at the beginning).

Can you check pls?

> Anyway lower MTU should work.

Manually tweaking MTU seems to be broken in lots of systems -
I sometimes see the same behaviour with gigabit ethernet.

> >As a side note, with 1.5K MTU it's probably better to use datagram mode
> >anyway.
> 
> Now I see that I missed that in the report. We used datagram mode.

Did you try checking ethernet BW on the same machine?


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