Caitlin Bestler wrote:
-----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.
posting a 0B read after the mpa setup isn't changing the MPA protocol.
Its adding a protocol on top of the MPA setup in order to meet the
requirements of the MPA protocol. Whether you add a private-data
request for this or _assume_ the 0B read will happen doesn't change this.
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