When and what to compile/optimize in a virtual machine?

• Authors: K. V. Seshu Kumar
• Venue: ACM SIGPLAN Notices
• Year: 2004

To speed up the computation of some of the object languages, virtual machines use dynamic compilation. But due to compilation taking place during user application runtime, one has to choose which methods to compile, so that the compile time has little impact on the total runtime of the actual application. In order to achieve this, we have to use an estimate to determine the process of compilation. Current virtual machines use run time information such as number of calls made to this method, size of the method and as well as number of times the back edges taken to determine the hotness of a method. They use this information against some threshold which does not have any relationship with the method that is being considered for compilation.Detecting the hot routines is very important from the perspective of performance since optimized methods run 10 times faster than the interpreted version. In this paper we propose a new technique called relative estimation for determining the hotness of the functions. For each method in the application, we estimate the cost/benefits for compilation or optimization by doing method analysis. We select the methods for compilation or optimization initially based on the above metrics using the proposed relative estimation technique. Later on we use the online profile information such as backedge counters and invocation counts to adjust the relative estimation process itself. We have performed experiments to validate the effectiveness of the proposed method on SPECjvm98 benchmark suite and found that up to 4% performance improvement in the application execution time occurs.