Preparing for Future Heterogeneous Systems Using Migrating Threads

Heterogeneity in computing systems is clearly increasing, especially as "accelerators" burrow deeper and deeper into different parts of an architecture. What is new, however, is a rapid change in not only the number of such heterogeneous processors, but in their connectivity to other structures, such as cores with different ISAs or smart memory interfaces. Technologies such as chiplets are accelerating this trend. This paper is focused on the problem of how to architect efficient systems that combine multiple heterogeneous concurrent threads, especially when the underlying heterogeneous cores are separated by networks or have no shared-memory access paths. The goal is to eliminate today's need to invoke significant software stacks to cross any of these boundaries. A suggestion is made of using migrating threads as the glue. Two experiments are described: using a heterogeneous platform where all threads share the same memory to solve a rich ML problem, and a fast PageRank approximation that mirrors the kind of computation for which thread migration may be useful. Architectural "lessons learned" are developed that should help guide future development of such systems.