Basic Usage

As of Linux 4.6, capturing kernel call stacks using perf_events from a non-root process requires setting two runtime variables. You can set them using sysctl or as follows:

# sysctl kernel.perf_event_paranoid=1
# sysctl kernel.kptr_restrict=0

To run the agent and pass commands to it, the helper script profiler.sh is provided. A typical workflow would be to launch your Java application, attach the agent and start profiling, exercise your performance scenario, and then stop profiling. The agent's output, including the profiling results, will be displayed in the Java application's standard output.

Example:

$ jps
9234 Jps
8983 Computey
$ ./profiler.sh start 8983
$ ./profiler.sh stop 8983

The following may be used in lieu of the pid (8983):

• The keyword jps, which will use the most recently launched Java process.
• The application name as it appears in the jps output: e.g. Computey

Alternatively, you may specify -d (duration) argument to profile the application for a fixed period of time with a single command.

$ ./profiler.sh -d 30 8983

By default, the profiling frequency is 100Hz (every 10ms of CPU time). Here is a sample of the output printed to the Java application's terminal:

--- Execution profile ---
Total samples:           687
Unknown (native):        1 (0.15%)

--- 6790000000 (98.84%) ns, 679 samples
  [ 0] Primes.isPrime
  [ 1] Primes.primesThread
  [ 2] Primes.access$000
  [ 3] Primes$1.run
  [ 4] java.lang.Thread.run

... a lot of output omitted for brevity ...

          ns  percent  samples  top
  ----------  -------  -------  ---
  6790000000   98.84%      679  Primes.isPrime
    40000000    0.58%        4  __do_softirq

... more output omitted ...

This indicates that the hottest method was Primes.isPrime, and the hottest call stack leading to it comes from Primes.primesThread.