It's just that providing a "more meaningful" key can help when debugging or managing through the OS. You still have to generate some sort of "sequence" number per-communicator, as successive allocations on the same communicator must return different memory. So, communicator alone is not enough to uniquely identify/select an allocation. Implementations will have to generate a "key" to pass to the OS, and so all ranks must be able to generate identical keys for corresponding calls. _______________________________________________ Douglas Miller BlueGene Messaging Development IBM Corp., Rochester, MN USA Bldg 030-2 A410 [email protected] Douglas Miller/Rochester/IBM Pavan Balaji <[email protected] ov> To [email protected] 12/07/2010 08:08 cc AM Douglas Miller/Rochester/IBM@IBMUS Subject Re: [Mpi3-hybridpm] Hybrid WG meeting at the Forum On 12/07/2010 07:58 AM, Douglas Miller wrote:
In order to ensure all nodes get the same memory segment, they all have to use the same "key". At least if this is implemented on Unix SysV or POSIX shmem. Then there's the possibility of some nodes allocing on a sub-comm first, etc. I think its just avoiding a lot of potential complications and don't see what the downside is.
In that sense, isn't the communicator a "key"? -- Pavan -- Pavan Balaji http://www.mcs.anl.gov/~balaji
