Hugo Taboada will defend his PhD thesis entitled “MPI Non-Blocking Collective Overlap on Manycore Processor” on Tuesday, December 11th at 10:00 AM.
Supercomputers used in HPC are composed of severals inter-connected machines. Usually, they are programmed using MPI which specify an API for messages exchanges between machines. To amortize the cost of MPI collective operations, non-blocking collectives have been proposed so as to allow communications to be overlapped with computation. Initially, these operations were only available for communication between 2 MPI processes : point-to-point communications. Non-blocking communications were expanded to collective communications in 2012 with MPI 3.0. This opens up the possibility to overlap non-blocking collective communications with computation. However, these operations are more CPU-hungry than point-to-point communications.
We propose to approach this problem from several angles. On the one hand, we focus on the placement of progress threads generated by the MPI non-blocking collectives. We propose two progress threads placements algorithms for all non-blocking collectives. We either bind them on free cores, or we bind them on the hyper-threads. Then, we focus on optimizing two types of algorithms used by collective operations: tree-based algorithms and chain-based algorithms.
On the other hand, we also study the scheduling of progress threads to avoid their execution when it is unecessary to the advancement of the collective algorithm. For that, we propose first to use a mechanism to suspend the scheduling of these threads, and then we force their optimal scheduling statically by using semaphores. Finally, we introduce a proof of concept scheduling policy with priorities.
The thesis is reported by :
George Bosilca, University of Tennessee, Knoxville
Christian Perez, Inria Grenoble Rhône-Alpes
The Jury is :
Emmanuel Jeannot (Inria Bordeaux Sud-Ouest)
Alexandre Denis (Inria Bordeaux Sud-Ouest)
Julien Jaeger (CEA)
Christian Perez (Inria Grenoble Rhône-Alpes)
Jean-Marc Pierson (Université de Toulouse)
Raymond Namyst (Université de Bordeaux)
Pascale Rossé-Laurent (Bull Atos)