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From: Jabe <jabe.chapman-9AbUPqfR1/2XDw4h08c5KA@public.gmane.org>
Subject: Re: [ewg] IPoIB to Ethernet routing performance
Date: Mon, 27 Dec 2010 12:51:13 +0100
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Cc: Richard Croucher <richard-jNDFPZUTrfRJpuwtbJ71GdBPR1lH4CV8@public.gmane.org>, 'Ali Ayoub' <ali-LDSdmyG8hGV8YrgS2mwiifqBs+8SCbDb@public.gmane.org>, 'Christoph Lameter' <cl-vYTEC60ixJUAvxtiuMwx3w@public.gmane.org>, 'linux-rdma' <linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, 'sebastien dugue' <sebastien.dugue-6ktuUTfB/bM@public.gmane.org>, 'OF EWG' <ewg-ZwoEplunGu1OwGhvXhtEPSCwEArCW2h5@public.gmane.org>
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On 12/26/2010 11:57 AM, Richard Croucher wrote:
> The vNIC driver only works when you have Ethernet/InfiniBand hardware
> gateways in your environment.   It is useful when you have external hosts to
> communicate with which do not have direct InfiniBand connectivity.
> IPoIB is still heavily used in these environments to provide TCP/IP
> connectivity within the InfiniBand fabric.
> The primary Use Case for vNICs is probably for virtualization servers, so
> that individual Guests can be presented with a virtual Ethernet NIC and do
> not lead to load any InfiniBand drivers.  Only the hypervisor needs to have
> the InfiniBand software stack loaded.
> I've also applied vNICs in the Financial Services arena, for connectivity to
> external TCP/IP services but there the IPoIB gateway function is arguably
> more useful.
>
> The whole vNIC arena is complicated by different, incompatible
> implementations from each of Qlogic and Mellanox.
>
> Richard
>    


Richard, with your explanation I understand why vNIC / EoIB is used in 
the case you cite, but I don't understand why it is NOT used in the 
other cases (like Ali says).

I can *guess* it's probably because with a virtual ethernet fabric you 
have to do all IP stack in software, probably without even having the 
stateless offloads (so it would be a performance reason). Is that the 
reason?

Thank you
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