Support for Interactive Low-Overhead Profiling

The profiling support we built into the Java virtual machine achieves the following two desirable goals:

• We must be able to support interactive profiler front-ends. An approach that only supports collecting profiling events into trace files does not meet the needs of programmers and tools vendors. The user must to enable and disable profiling events during program execution in order to pinpoint performance problems in different stages of running an application.
• The profiling support must incur low overhead so that programmers can run the application at full speed when profiling events are disabled, and only pay for the overhead of generating the type of events specifically requested by the profiler front-end. An approach that requires the use of a less optimized virtual machine implementation for profiling leads to additional discrepancies between the profiled environment and real-world scenarios.

Because of the low overhead of our approach, we are able to provide full profiling support in the standard deployed version of the Java virtual machine implementation. It is possible to start an application normally, and enable the necessary profiling events later without restarting the application.