This logging should be deployed with the released application. Performance logging should not produce more than one line of output to a log file per 20 seconds. Ideally your logging framework should be designed so that the output can be used in other tools for easy manipulation and analysis. Unit performance tuning proceeds by integrating the unit into the system simulation and running scaling tests with profiling. It's important to test the full system or simulation as soon as is feasible, even if many of the units are incomplete.
Simulated units are acceptable at an early stage of system performance testing.
Later the tests should provide detailed logs and profiles that will allow developers to target bottlenecks in the system and produce faster versions of the application. To support performance testing at later stages, the testbed should be able to be configured to provide performance profiles of any JVM processes, as well as system and network statistics in addition to performance logging. Your performance experts should be able to produce the JVM profiles. Ideally, a system administrator already has those skills. The performance tests should scale to higher loads of users and data.