[Mpi3-ft] system-level C/R requirements

[Joseph Ruscio]

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