> -----Original Message----- > From: Steve Wise [mailto:[EMAIL PROTECTED] > Sent: Tuesday, November 27, 2007 4:48 PM > To: Caitlin Bestler > Cc: Kanevsky, Arkady; Glenn Grundstrom; Leonid Grossman; openib- > [EMAIL PROTECTED] > Subject: Re: [ofa-general] Re: iWARP peer-to-peer CM proposal > > Caitlin Bestler wrote: > > On Nov 27, 2007 3:58 PM, Steve Wise <[EMAIL PROTECTED]> > 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. >
That is an extra round-trip per connection setup, which is a significant penalty for a short lived connection. It is trivial for HPC/peer-to-peer applications, but would be a killer for something like HTTP over RDMA. Doing something like this for *every* connection makes it effectively a change to the MPA protocol. OFA is not the forum for such discussions, the IETF is. OFA drafting an understanding of how peer-to-peer applications use the existing protocol, on the other hand, is quite reasonable. But it has to be something done by peer-to-peer middleware or by the verbs layer in response to a flag from the peer-to-peer middleware. Otherwise it is not augmenting a protocol, it is changing it.
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