[openib-general] dapl broken for iWARP

[Kanevsky, Arkady]

That is correct.
I am working with Krishna on it.
Expect patches soon.

By the way the problem is not DAPL specific
and so is a proposed solution.

There are 3 aspects of the solution.
One is APIs. We suggest that we do not augment these.
That is a connection requestor sets its QP
RDMA ORD and IRD.
When connection is established user can check the QP RDMA ORD and IRD
to see what he has now to use over the connection.
We may consider to extend QP attributes to support transport specific
parameters passing in the future.
For example, iWARP MPA CRC request.

Second is the semantic that CM provides.
The proposal is to match IBCM semantic.
That is CM guarantee that local IRD is >= remote ORD.
This guarantees that incoming RDMA Read requests will not overwhelm
the QP RDMA Read capabilities.
Again there is not changes to IBCM only to IWCM.
Notice that as part of this IWCM will pass down to driver and extract
from driver
needed info.

The final part is iWARP CM extension to exchange RDMA ORD, IRD.
This is similar to IBTA Annex for IP Addressing.
The harder part that this will eventually require IETF MPA spec
extension,
and the fact that MPA protocol is implemented in RNIC HW by many
vendors,
and hence can not be done by IWCM itself.

Thanks,

Arkady Kanevsky                       email: arkady at netapp.com
Network Appliance Inc.               phone: 781-768-5395
1601 Trapelo Rd. - Suite 16.        Fax: 781-895-1195
Waltham, MA 02451                   central phone: 781-768-5300
 

> -----Original Message-----
> From: Steve Wise [mailto:swise at opengridcomputing.com] 
> Sent: Wednesday, February 07, 2007 6:12 PM
> To: Arlin Davis
> Cc: openib-general
> Subject: Re: [openib-general] dapl broken for iWARP
> 
> On Wed, 2007-02-07 at 15:05 -0800, Arlin Davis wrote:
> > Steve Wise wrote:
> > 
> > >On Wed, 2007-02-07 at 14:02 -0600, Steve Wise wrote:
> > >  
> > >
> > >>Arlin,
> > >>
> > >>The OFED dapl code is assuming the responder_resources and 
> > >>initiator_depth passed up on a connection request event 
> are from the 
> > >>remote peer.  This doesn't happen for iWARP.  In the 
> current iWARP 
> > >>specifications, its up to the application to exchange this 
> > >>information somehow. So these are defaulting to 0 on the 
> server side 
> > >>of any dapl connection over iWARP.
> > >>
> > >>This is a fairly recent change, I think.  We need to come up with 
> > >>some way to deal with this for OFED 1.2 IMO.
> > >>    
> > >>
> > Yes, this was changed recently to sync up with the rdma_cm changes 
> > that exposed the values.
> > 
> > >>    
> > >>
> > >
> > >The IWCM could set these to the device max values for instance.
> > >  
> > >
> > That would work fine as long as you know the remote 
> settings will be 
> > equal or better. The provider just sets the min of local device max 
> > values and the remote values provided with the request.
> > 
> 
> I know Krishna Kumar is working on a solution for exchanging 
> this info in private data so the IWCM can "do the right 
> thing".  Stay tuned for a patch series to review for this.  
> But this functionality is definitely post OFED-1.2.  
> 
> 
> So for the OFED-1.2, I will set these to the device max in the IWCM.
> Assuming the other side is OFED 1.2 DAPL, then it will work fine.
> 
> Steve.
> 
> 
> 
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