Pyflame

Pyflame is a tool for generating flame graphs for Python processes. Pyflame is different from existing Python profilers because it doesn't require explicit instrumentation -- it will work with any running Python process! Pyflame works by using the ptrace(2) system call to analyze the currently-executing stack trace for a Python process.

Read the Uber Engineering blog post about Pyflame here.

Installing

To build Pyflame you will need a C++ compiler with basic C++11 support. Pyflame is known to compile on versions of GCC as old as GCC 4.6. You'll also need GNU Autotools (GNU Autoconf and GNU Automake) if you're building from the git repository.

From git you would compile like so:

./autogen.sh
./configure      # plus any options like --prefix
make
make install

Fedora

The following command should install the necessary packages to build on Fedora:

sudo dnf install autoconf automake gcc-c++ python-devel

Debian

The following command should install the necessary packages to build on Debian (or Ubuntu):

sudo apt-get install autoconf autotools-dev g++ pkg-config python-dev

If you'd like to build a Debian package there's already a debian/ directory at the root of this project. We'd like to remove this, as per the upstream Debian packaging guidelines. If you can help get this project packaged in Debian please let us know.

Usage

After compiling Pyflame you'll get a small executable called pyflame. The most basic usage is:

# profile PID for 1s, sampling every 1ms
pyflame PID

The pyflame command will send data to stdout that is suitable for using with Brendan Gregg's flamegraph.pl command (which you can get here). Therefore a typical command pipeline might be like this:

# generate flame graph for pid 12345; assumes flamegraph.pl is in your $PATH
pyflame 12345 | flamegraph.pl > myprofile.svg

You can also change the sample time and sampling frequency:

# profile PID for 60 seconds, sampling every 10ms
pyflame -s 60 -r 0.10 PID

FAQ

What Is "(idle)" Time?

From time to time the Python interpreter will have nothing to do other than wait for I/O to complete. This will typically happen when the Python interpreter is waiting for network operations to finish. When that happens Pyflame will report the time as "idle".

If you don't want to include this time you can use the invocation pyflame -x.

What Are These Ptrace Permissions Errors?

To run Pyflame you'll need appropriate permissions to PTRACE_ATTACH the process. Typically this means that you'll need to invoke pyflame as root, or as the same user as the process you're trying to profile. If you have errors running it as the correct user then you probably have ptrace_scope set to a value that's too restrictive.

Debian Jessie ships with ptrace_scope set to 1 by default, which will prevent unprivileged users from attaching to already running processes. This will also manifest by being unable to use gdb -p as an unprivileged user by default.

To see the current value of this setting:

sysctl kernel.yama.ptrace_scope

If you see a value other than 0 you may want to change it. Note that by doing this you'll affect the security of your system. Please read the relevant kernel documentation for a comprehensive discussion of the possible settings and what you're changing. If you want to completely disable the ptrace settings and get "classic" permissions (i.e. root can ptrace anything, unprivileged users can ptrace processes with the same user id) then use:

# use this if you want "classic" ptrace permissions
sudo sysctl kernel.yama.ptrace_scope=0

Python 3 Support

There is very basic Python 3 support, which you can get by compiling using:

./configure --with-python=python3

This should work as long as none of your files have non-ASCII characters in their names. If you are interested in supporting Unicode file names please assist us with pull requests.

Legal and Licensing

Pyflame is free software licensed under the Apache License, Version 2.0.

marktheunissen/pyflame