Just to correct one comment:
A ULP written to TCP/IP can use RDMA transport without change. An example is SDP not that the ULP must use what SDP uses. Also, please keep in mind that SDP on iWARP uses the port mapper protocol to obtain the IP address and port to target for the connection request. So, the TCP connection establishment is to the RDMA listen endpoint from the start and the SDP hello exchange then fills in the rest of the parameters required to determine whether the connection should proceed and what resources should be configured when the response is generated.
I will also re-iterate what another person stated and that is to separate out the interface from the wire protocol. IBTA defines wire protocols / semantics while OpenIB is defining its API to communicate the wire protocol and associated semantics. I agree with that person on this point and their other point on the need for the IBTA to construct a solid spec for the wire protocol and associated semantics. OpenIB will then determine how best to implement but these are separate efforts and it would be more productive for all to table the discussion for now. The original request was whether something would break if the private data size was changed. It was noted that one cannot know what will or will not break thus the requirement is to provide a method for software to note the difference in the layout. How is for the IBTA to specify.
Just a thought......
Mike
At 03:43 PM 10/25/2005, Sean Hefty wrote:
Kanevsky, Arkady wrote:
What are you trying to achieve?
I'm trying to define a connection *service* for Infiniband that uses TCP/IP addresses as its user interface. That service will have its own protocol, in much the same way that SDP, SRP, etc. do today.
I am trying to define an IB REQ protocol extension that
support IP connection 5-tuple exchange between connection
requestor and responder.
Why? What need is there for a protocol extension to the IB CM? To me, this is similar to setting a bit in the CM REQ to indicate that the private data format looks like SDP's private data. The format of the _private_ data shouldn't be known to the CM; that's why it's private data.
And define mapping between IP 5-tuple and IB entities.
No mapping between IP <-> IB addresses was defined in the proposal. Defining this mapping is required to make this work. Right now, the mapping is the responsibility of every user.
That way ULP which was written to TCP/IP, UDP/IP, CSTP/IP (and so on)
can use RDMA transport without change.
A ULP written to TCP/IP can use an RDMA transport without change. They use SDP. However, an application that wants to take advantage of QP semantics must change. (And if they want to take full advantage of RDMA, they'll likely need to be re-architected as well.) The goal in that case becomes to permit them to establish connections using TCP/IP addresses.
To meet this goal, we need to define how to map IP address to and from IB addresses. That mapping is part of the protocol, and is missing from the proposal. And if the application isn't going to know that they're running on Infiniband, then the mapping must also include mapping to a destination service ID.
To modify ULP to know that it runs on top of IB vs. iWARP
vs. (any other RDMA transport) is bad idea.
It is one thing to choose proper port to connect.
Completely different to ask ULP to parse private data
in transport specific way.
The same protocol must support both user level ULPs
and kernel level ULPs.
Defining an interface that allows a ULP to use either iWarp, IB, or some other random RDMA transport is an implementation issue. However, it requires something that maps IP to IB addresses (including service IDs).
To be more concrete, you've gone from having source and destination TCP/IP addresses to including them in a CM REQ. What translated the source and destination IP addresses into GIDs and a PKey? Who converted those into IB routing information? How was the destination of the CM REQ determined? What service ID was selected?
- Sean
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