On 7/14/06 10:40 AM, "Michael Kluskens" <mklusk...@ieee.org> wrote:
> I've looked through the documentation but I haven't found the > discussion about what each BTL device is, for example, I have: > > MCA btl: self (MCA v1.0, API v1.0, Component v1.2) This is the "loopback" Open MPI device. It is used exclusively for sending and receiving from one process to the same process. I.e., message passing is effected by memcpy's in the same process -- no network is involved (not even shared memory, because it's within a single process). We do this not for optimization, but rather for software engineering reasons -- by having a "self" BTL, all the other BTLs can assume that they never have to handle the special case of "sending/receiving to self". > MCA btl: sm (MCA v1.0, API v1.0, Component v1.2) This is shared memory. It is used to communicate between processes on the same node. > MCA btl: tcp (MCA v1.0, API v1.0, Component v1.0) I think this one is pretty obvious. ;-) > I found a PDF presentation that describes a few: > > tcp - TCP/IP > openib Infiniband OpenIB Stack > gm/mx- Myrinet GM/MX > mvapi - Infiniband Mellanox Verbs > sm - Shared Memory > > Are there any others I may see when interacting with other people's > computers? These are the main ones for now. There may be more in the future. > I assume that if a machine has Myrinet and I don't see MCA btl: gm or > MCA btl: mx then I have to explain the problem to the sysadm's. Correct. > The second question is should I see both gm & mx, or only one or the > other. Probably just one or the other; I *believe* that you cannot have both installed on the same node. That being said, you can have the *support libraries* for both installed on the same node and therefore Open MPI can build support for it and show that those btl's exist in the output of ompi_info. But only one will *run* at a time. Sorry for the delay on the answer -- hope this helps! -- Jeff Squyres Server Virtualization Business Unit Cisco Systems
