Faster Work Stealing With Return Barriers

Work-stealing is a promising approach for effectively exploiting software parallelism on parallel hardware. A programmer who uses work-stealing explicitly identifies potential parallelism and the runtime then schedules work, keeping otherwise idle hardware busy while relieving overloaded hardware of its burden. However, work-stealing comes with substantial overheads. Our prior work demonstrates that using the exception handling mechanism of modern VMs and gathering the runtime information directly from the victim’s execution stack can significantly reduce these overheads. In this paper we identify the overhead associated with managing the work-stealing related information on a victim’s execution stack. A return barrier is a mechanism for intercepting the popping of a stack frame, and thus is a powerful tool for optimizing mechanisms that involve scanning of stack state. We present the design and preliminary findings of using return barriers on a victim’s execution stack to reduce these overheads. We evaluate our design using classical work-stealing benchmarks. On these benchmarks, compared to our prior design, we are able to reduce the overheads by as much as 58%. These preliminary findings give further hope to an already promising technique of harnessing rich features of a modern VM inside a work-stealing scheduler.