The Chapel Tasking Layer Over Qthreads

This paper describes the applicability of the third-party qthread lightweight threading library for implementing the tasking layer for Chapel applications on conventional multisocket multicore computing platforms. A collection of Chapel benchmark codes were used to demonstrate the correctness of the qthread implementation and the performance gain provided by using an optimized threading/tasking layer. The experience of porting Chapel to use qthreads also provides insights into additional requirements imposed by a lightweight user-level threading library, some of which have already been integrated into Chapel, and others that are posed here as open issues for future work. The initial performance results indicate an immediate performance benefit from using qthreads over the native multithreading support in Chapel. Both task and data parallel applications benefit from lower overheads in thread management. Future work on improved synchronization semantics are likely to further increase the efficiency of the qthreads implementation.