Debugging large scale applications in a virtualized environment

With the advent of petascale machines with hundreds of thousands of processors, debugging parallel applications is becoming an increasing challenge. Aside from the complicated debugging techniques required to debug applications at such scale, it is often difficult to gain access to these machines for a sufficient period of time, if at all. Some existing parallel debuggers are capable of handling these machines, but they still require the whole machine to be allocated. In this paper, we present an innovative approach to address debugging on such extreme scales. By leveraging the concept of object-based processor virtualization, our technique enables debugging of even a million processor execution under a simulated environment using only a relatively small cluster. We describe the obstacles we overcame to achieve this goal within two message passing programming models: Charm++ and MPI. We demonstrate the results using real world applications such as Molecular Dynamics and Cosmological simulation programs.