Dynamic Compilation: The Benets of Early Investing

Dynamic compilation is typically performed in a separate thread, asynchronously with the remaining application threads. This com-pilation thread is often scheduled for execution in a simple round-robin fashion either by the operating system or by the virtual ma-chine 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 asyn-chronous dynamic compilation in a virtual machine. We begin by describing the shortcomings of current approaches and demon-strate their potential to perform poorly under certain conditions. We describe the importance of enforcing a minimum level of uti-lization for the compilation thread, and evaluate the performance implications of varying the utilization that is enforced. We ob-served 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