Dynamic Compilation: The Benefits Of Early Investing

Dynamic compilation is typically performed in a separate thread, asynchronously with the remaining application threads. This compilation thread is often scheduled for execution in a simple round-robin fashion either by the operating system or by the virtual machine itself. Despite the popularity of this approach in production virtual machines, it has a number of shortcomings that can lead to suboptimal performance.This paper explores a number of issues surrounding asynchronous dynamic compilation in a virtual machine. We begin by describing the shortcomings of current approaches and demonstrate their potential to perform poorly under certain conditions. We describe the importance of enforcing a minimum level of utilization for the compilation thread, and evaluate the performance implications of varying the utilization that is enforced. We observed surprisingly large speedups by increasing the priority of the compilation thread, averaging 18.2% improvement over a large benchmark suite. Finally, we discuss options for implementing these techniques in a VM and address relevant issues when moving from a single-processor to a multiprocessor machine.