Checkpointing OpenSHMEM Programs Using Compiler Analysis

The importance of fault tolerance continues to increase for HPC applications. The continued growth in size and complexity of HPC systems, and of the applications themselves, is leading to an increased likelihood of failures during execution. However, most HPC programming models do not have a built-in fault tolerance mechanism. Instead, application developers usually rely on external support such as application-level checkpoint-restart (C/R) libraries to make their codes fault tolerant. However, this increases the burden on the application developer, who must use the libraries carefully to ensure correct behavior and to minimize the overheads. The C/R routines will be employed to save the values of all needed program variables at the places in the code where they are invoked. It is important for correctness that the program data is in a consistent state at these places. It is non-trivial to determine such points in OpenSHMEM, which relies upon single-sided communications to provide high performance. The amount of data to be collected, and the frequency with which this is performed, must also be carefully tuned, as the overheads introduced by C/R calls can be extremely high. There is very little prior work on checkpoint-restart support in the context of the OpenSHMEM programming interface. In this paper, we introduce OpenSHMEM and describe the challenges it poses for checkpointing. We identify the safest places for inserting C/R calls in an OpenSHMEM program and describe a straightforward approach for identifying the data that needs to be checkpointed at these positions in the code. We provide these two functionalities in a tool that exploits compiler analyses to propose checkpoints and the sets of data for saving at them, to the application developer.