Add PyPerf, example of profiling Python using BPF

[palmtenor]

This is a tool attaches BPF program to CPU Perf Events for profiling. The BPF program understands CPython internal data structure and hence able to walk actual Python stack-trace, as oppose to strac-trace of the CPython runtime itself as we would normally get with Linux perf.

To use the tool, just run the PyPerf binary:

• Use -d / --duration to specify intended profiling duration, in milliseconds. Default value, if not specified, is 1000ms.
• Use -c / --sample-rate to specify intended profiling sample rate, same as -c argument of Linux perf. Default value, if not specified, is 1e6.

You can also use -v / --verbose to specify logging verbosity 1 or 2 for more detailed information during profiling.

The tool is a prototype at this point is by no mean mature. It currently has follow limitation:

• It only runs on CPU Cycles event.
• It only works on Python 3.6 at this point. In fact all Python version from 3.0 to 3.6 should work, I just need to verify and change the constant value. However in Python 3.7 there are some internal data structure changes that the actual parsing logic needs to be updated.
• It currently hard-codes the Python internal data structure offsets. It would be better to get a dependency of python-devel and get them directly from the header files.
• The output is pretty horrible. No de-duplication across same stack, and we always output the GIL state, Thread state and output them in raw integer value. I will need to work on prettifying the output and make better sense of the enum values.

Landing it in C++ example for now, once it's mature enough I will move it to tools/.

Feel free to try it out and let me know what do you think!

[yonghong-song]

I tried the following example,

-bash-4.4$ vi test.py
-bash-4.4$ cat test.py
def mul_helper(x):
  while True:
    x*x

def mul(x):
  mul_helper(x)

mul(10000)
-bash-4.4$ python3 test.py

And running

-bash-4.4$ pwd
/home/yhs/work/bcc/build/examples/cpp/pyperf
-bash-4.4$ sudo ./PyPerf -d 4

I got the following result:

...
GIL State: 1 Thread State: 2 PthreadID Match State: 1

    test.mul_helper
    test.mul
    test.<module>
PID: 771568 TID: 771568 (python3)

What does "GIL State: 1 Thread State: 2 PthreadID Match State: 1" mean?
Do agree that we need to do a better job to present the meaningful info here.

Anyway, this is a good start. It is in examples/. People can try and the tool can evolve.

thanks!