Re: [PATCH 1/3] rdma_cm: Add support for a new RDMA_PS_LUSTRE Lustre port space

[sebastien dugue <sebastien.dugue-6ktuUTfB/bM@public.gmane.org>]

  Hi Roland,

On Tue, 19 Jan 2010 17:12:43 -0800
Roland Dreier <rdreier-FYB4Gu1CFyUAvxtiuMwx3w@public.gmane.org> wrote:

> 
>  >   Well, without a specific port space, the default for Lustre is to use the
>  > TCP port space so you cannot distinguish Lustre traffic from other traffic using
>  > that same port space.
> 
> I'm still a bit confused.  The problem as I understand it is that Lustre
> always uses the same TCP port, so there's no way to apply different QoS
> to different types of Lustre traffic.

  Right, all Lustre servers (MDS and OSS) use the same TCP port, so there's no
way to distinguish between the 2 types of traffic.

>  But if we create a new port space
> and don't change the ports that Lustre uses, then there's still no way
> to apply different QoS for different Lustre traffic.

  With the OpenSM patch and the Lustre port space, you can map Lustre traffic
to specific target port GUIDs onto a specific SL hence separating the flows.

>  So I guess you
> need to change the ports used within the new port space -- but then why
> can't you just stay in the TCP space but change the ports used?

  No, with the new port space, there's no need to change ports. You only need
to specify the target GUIDs.

  For example:

    qos-­ulps 
        default                 	      : 0 # default SL
        lustre, target-­port­guid 0x1234,0x1235 : 1 # lustre traffic to MDSs
        lustre                  	      : 2 # default lustre traffic (to OSSs)
    end­-qos-­ulps


  Hope this helps clarify things a bit.

  Thanks,

  Sébastien.




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