On Oct 27, 2008, at 7:18 AM, Thomas Herault wrote:

So, my question is: what are the benefits of solution b) as compared to solution a)?

If you go with solution b), the only thing the MPI implementation needs to worry about is PREPAREing and RESTOREing the network state. All of the checkpoint specific issues and complexity such as queuing system integration, checkpoint file storage options like redundant local storage, etc. In case a), MPI implementations need to concern themselves with these issues AND support the non-standard checkpoint invocation API's for every different desired system checkpointer. So that's a question of whether the responsibility for system-level checkpointer integration lays on the MPI implementor or the individual checkpoint implementors. Going with b) gives MPI an opportunity to minimally specify an integration mechanism with system-level checkpointer's. If the MPI implementor does not wish to worry about these classes of CP/R systems, they just don't implement the minimal set of calls. If they do want the support, they implement the calls. A single implementation of PREPARE and RESTORE would support most system-level checkpointers. For example our checkpointer that sits completely in user-land and BLCR that sits completely in the OS would have the same set of requirements. VMM level checkpointers have been suggested as being different. Wouldn't they either have the same requirements, or be completely transparent to the MPI stack i.e. snapshotting the OS, communication device, etc and allowing the protocol to sort out lost messages? cheers, Joe