Relational profiling: enabling thread-level parallelism in virtual machines

Virtual machine service threads can perform many tasks in parallel with program execution such as garbage collection, dynamic compilation, and profile collection and analysis. Hardware-assisted profiling is essential for providing service threads with needed information in a flexible and efficient way. A relational profiling architecture (RPA) is proposed for meeting this goal. The RPA selects particular instructions for profiling, and communicates collected information to service threads through shared memory message queues. The RPA's capabilities lead to new profiling applications, such as concurrent garbage collection. Simulations indicate that a low-cost implementation of the RPA should be able to profile four in-flight instructions simultaneously, and provide storage for eight profile records. Profiling overhead is less than 0.5% for concurrent garbage collection and edge profiling.