[ofa-general] Re: iWARP peer-to-peer CM proposal

[Steve Wise]

Caitlin Bestler wrote:
> On Nov 27, 2007 3:58 PM, Steve Wise <swise at opengridcomputing.com> wrote:
> 
>> For the short term, I claim we just implement this as part of linux
>> iwarp connection setup (mandating a 0B read be sent from the active
>> side).  Your proposal to add meta-data to the private data requires a
>> standards change anyway and is, IMO, the 2nd phase of this whole
>> enchilada...
>>
>> Steve.
>>
> 
> I don't see how you can have any solution here that does not require meta-data.
> For non-peer-to-peer connections neither a zero length RDMA Read or Write
> should be sent. An extraneous RDMA Read is particularly onerous for a short
> lived connection that fits the classic active/passive model. So *something*
> is telling the CMA layer that this connection may need an MPA unjam action.
> If that isn't meta-data, what is it?

I assumed the 0B read would _always_ be sent as part of establishing an 
iWARP connection using linux and the rdma-cm.

> 
> Further, the RDMA Read solution is adequate whenever the RDMA Write
> solution would have been (although at an unnecessary extra cost), but
> as near as I can determine it is not a complete solution. If the passive
> side needs an untagged message completion then *something* needs
> to send it. How can the CM layer (or, I suppose, the ULP itself) know
> that this untagged NOP message must be sent without meta-data?

I believe at Reno we had the current rnic vendors all saying a SEND or 
0B read will work.  So:  If someone has current iwarp HW that will _not_ 
  handle this problem by doing the 0B read hack, please speak up now.

> 
> As I see it, if we want to do the minimum that is required, but be certain
> that it is adequate, we need a per-connection setup meta-data exchange.

Are you going to prototype this?


Steve.