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

[Caitlin Bestler]

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?

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?

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.