Toucan — A Translator for Communication Tolerant MPI Applications

We discuss early results with Toucan, a source-to-source translatorthat automatically restructures C/C++ MPI applications tooverlap communication with computation. We co-designed thetranslator and runtime system to enable dynamic, dependence-drivenexecution of MPI applications, and require only a modest amount ofprogrammer annotation. Co-design was essential to realizingoverlap through dynamic code block reordering and avoiding the limitations of static code relocation and inlining. We demonstrate that Toucan hides significantcommunication in four representative applications running on up to 24Kcores of NERSC's Edison platform. Using Toucan, we have hidden from 33% to 85% of the communication overhead, with performance meeting or exceeding that of painstakingly hand-written overlap variants.