Python profiling¶

This is a python profiling primer.

For the purpose of this document, qubes-dev is name of the domain used for postprocessing profiling stats.

Requirements¶

yum install gprof2dot graphviz
git clone http://git.woju.eu/qubes/profiling.git

If you profile something in dom0, move Upload.sh from the repository to dom0:

mkdir -p ~/profiling
qvm-run -p qubes-dev 'cat ~/profiling/Upload.sh' > ~/profiling/Upload.sh

WARNING: this will obviously be running third-party code which is not signed by ITL nor Fedora. You have been warned.

Workflow¶

Identify function responsible for some slow action¶

You have to select the area in which you suspect less than optimal performance. If you do not narrow the area, graphs may be unreadable.

Replace suspect function with probe¶

Replace

def foo(self, bar):
    # function content

with

def foo(self, *args, **kwargs):
    profile.runctx('self.real_foo(*args, **kwargs)', globals(), locals(),
        time.strftime('/home/user/profiling/foo-%Y%m%d-%H%M%S.pstats'))

def real_foo(self, bar):
    # function content

Run application¶

Beware that some functions may be called often. For example qubesmanager/main.py:update_table gets run once per second. This will produce one pstat file per second.

Remember to revert your changes to the application afterwards.

Upload statistics¶

If you are in dom0:

cd ~/profiling
./Upload.sh

Analyse¶

make

For every ${basename}.pstats this will produce ${basename}.txt and ${basename}.svg. SVG files contain call graphs. Text files contain lists of all functions, sorted by cumulative execution time. You may also try make all-png.

make index.html

This creates index.html with all SVG graphics linked to TXT files, ready for upload.

make REMOTE=example.com:public_html/qubes/profiling/ upload

Example¶

This example is from qubes-manager (qubesmanager/main.py).

It is apparent that the problem is around get_disk_usage, which calls something via subprocess.call. It does this 15 times, probably once per VM.