Chapel-on-X: Exploring Tasking Runtimes for PGAS Languages

Abstract

With the shift to exascale computer systems, the importance of productive programming models for distributed systems is increasing. Partitioned Global Address Space (PGAS) programming models aim to reduce the complexity of writing distributed-memory parallel programs by introducing global operations on distributed arrays, distributed task parallelism, directed synchronization, and mutual exclusion. However, a key challenge in the application of PGAS programming models is the improvement of compilers and runtime systems. In particular, one open question is how runtime systems meet the requirement of exascale systems, where a large number of asynchronous tasks are executed. While there are various tasking runtimes such as Qthreads, OCR, and HClib, there is no existing comparative study on PGAS tasking/threading runtime systems. To explore runtime systems for PGAS programming languages, we have implemented OCR-based and HClib-based Chapel runtimes and evaluated them with an initial focus on tasking and synchronization implementations. The results show that our OCR and HClib-based implementations can improve the performance of PGAS programs compared to the existing Qthreads backend of Chapel.