[ofw] patch: [ibbus] Add A new function to IBAL that allows one to create a multicast group without attaching a QP to it.

[Fab Tillier]

Hi Tzachi,

If we're talking about refactoring IPoIB, I'd suggest looking at statically allocating the CQ and QP when the adapter is created, and only modifying the state based on various PnP events.  The fact that we have this shadow 'port' object that contains the IB resources, that gets blown away and recreated whenever some error is detected is painful.  It also causes the QPN (and hence the MAC) to change whenever an error occurs.  If we had the QP up front, the only reason we'd have to change it would be a catastrophic failure, in which case a MAC address change would IMO be acceptable.

I think we could reduce the number of PnP events we need to handle if we allocated resource once, up front.  We'd have to handle port state changes and SM reregister.  Are there any others?  If these are the only events we need, we could get them directly from the HCA driver via the RDMA interface, and avoid all IBAL PnP interactions?

Thoughts?
-Fab

-----Original Message-----
From: ofw-bounces at lists.openfabrics.org [mailto:ofw-bounces at lists.openfabrics.org] On Behalf Of Tzachi Dar
Sent: Thursday, February 10, 2011 12:51 PM
To: Hefty, Sean; ofw at lists.openfabrics.org
Subject: Re: [ofw] patch: [ibbus] Add A new function to IBAL that allows one to create a multicast group without attaching a QP to it.

I guess that one example for your question can be the ipoib spec. According to this spec someone has to create the broadcast group. I guess that this is usually the SM, or some ipoib client, but we wanted to give freedom to other clients to create the group.

In a more practical way, what we want to achieve is a change to the current ipoib design. We would like to separate the qps life cycle from the multicast group. In the current code we had to make sure that the qp is always there before we can attach to the group.

Please note that adding a "dummy qp" when attaching to the multicast will hurt performance. (If we post receive buffers on the QP, than the hw will have to copy each packet twice. If we do not post receive buffers than this causes a fw flow that also creates performance hits.)

We consider this change as a first part, after which we will add functions that will allow us to attach/detach qps to the multicast group.

Thanks
Tzachi



> -----Original Message-----
> From: Hefty, Sean [mailto:sean.hefty at intel.com]
> Sent: Thursday, February 10, 2011 7:13 PM
> To: Tzachi Dar; ofw at lists.openfabrics.org
> Subject: RE: [ofw] patch: [ibbus] Add A new function to IBAL that allows one
> to create a multicast group without attaching a QP to it.
> 
> > On some occasions one might have to create a multicast group but does not
> > want to attach a QP to it.
> >
> > Any comments (including to function names) are welcomed.
> 
> Can you explain such an occasion where a node wants to join a multicast group,
> but never use it?
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