[dat-discussions] [openib-general][RFC]DAT2.0immediatedataproposal

[Kanevsky, Arkady]

We need a better job coordinating between 2 reflectors.

The current position is that DAT provide transport independent
API. We agreed on 2 Transport extensions, one for IB and one for iWARP,
that will be a separate documents. DAT proper will have hooks
to support extensions.
Currently, IB extensions include RDMA Write with immediate and Atomic
ops, and IW extension Socket connection model.

Also we have an advice to Consumer how to do things in Transport
independent way to make code portable, albeit at the cost of some
performance.

Feel free,
to review the current drafts of uDAPL 2.0, IB extension and IW extension
on DAT reflector or in the enclosed files.

Thanks,
Arkady


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: Tom Tucker [mailto:tom at opengridcomputing.com] 
> Sent: Thursday, April 20, 2006 9:34 PM
> To: Sean Hefty
> Cc: 'Roland Dreier'; dat-discussions at yahoogroups.com; 
> openib-general at openib.org
> Subject: RE: [dat-discussions] 
> [openib-general][RFC]DAT2.0immediatedataproposal
> 
> On Wed, 2006-02-08 at 23:20 -0800, Sean Hefty wrote:
> > >Hmm.  Can you put a number on how much better RDMA write with 
> > >immediate is on current HCA hardware?  How does using the 
> underlying 
> > >OpenIB verbs ability to post a list of work requests compare (ie 
> > >posting an RDMA write followed by a send in one verbs call)?
> > >Maybe "post multiple" is a better direction for DAT.
> > 
> > A "post multiple" call as a general API makes sense, but I think 
> > that's a separate issue.
> > 
> > Given that IB provides true immediate data with RDMA writes, a way 
> > should be available to make use of it.  I don't know what the 
> > performance numbers between using a write with immediate versus a 
> > write followed by a send, but I don't think that anyone could argue 
> > that the write with immediate wouldn't perform better.
> > 
> > To me, the question is whether write with immediate is 
> supported as a 
> > transport specific extension, which was Arlin's original patch, or 
> > through some standard API.  The attempt to make the API 
> standard, so 
> > that iWarp could emulate it (poorly in my view), is what 
> appears to be driving the disagreements.
> > 
> > It also appears to me that the decisions are coming down to 
> one of the 
> > following.  If iWarp can emulate write with immediate, then 
> a generic 
> > API should be used.
> 
> This opens Pandora's box. Should iWARP also emulate ATOMICs? 
> Which should be emulated and which should not ... What are 
> the criteria for deciding? 
> 
> > If iWarp cannot properly emulate write with immediate, then the API 
> > should be transport specific.
> 
> It should be transport specific because it is a transport 
> specific feature. Although -- in this case -- it could but 
> implemented in iWARP in my view it _should_ not. 
> 
> > It's curious to me that in both cases, iWarp is driving the API 
> > decision and design for something that is an IB specific feature.
> 
> Huh?
> 
> > 
> > - Sean
> > 
> > 
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> > 
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