On May 15, 2008, at 5:55 AM, Torje Henriksen wrote:
1. In the BTL SM component (both in "ompi_info --param btl sm" and the source), there is mention of RDMA. Is RDMA used in ths component? Is any special hardware needed for using it?
No and no. The SM BTL uses a copyout/copyin mechanism (copy out to shared memory, copy in to the target process) -- it does not directly copy from one process to another.
The OB1 PML uses "RDMA-like" semantics; I'm guessing that's what it's referring to.
2. As for eager vs non-eager messages. Is the only difference between these the amount of memory allocated for a fragment? Is there any rendevouz protocol used for large messages or anything like that?
The rendesvouz protocol is enforced by the upper level PML (OB1) -- it is basically the lower-layer-independent "protocol engine". OB1 decides the exact protocol to use (short, long, pipelined, etc.), and the lower later BTLs decide how to get the bits there.
The module based architecture is great, but sometimes I find it hard to figure out what is happening :)
Indeed. This is definitely a tradeoff when you only see small pieces of the puzzle at a time. :-\
-- Jeff Squyres Cisco Systems
