Coz: Causal Profiling

Causal profiling is a novel technique to measure optimization potential. This measurement matches developers' assumptions about profilers: that optimizing highly-ranked code will have the greatest impact on performance. Causal profiling measures optimization potential for serial, parallel, and asynchronous programs without instrumentation of special handling for library calls and concurrency primitives. Instead, a causal profiler uses performance experiments to predict the effect of optimizations. This allows the profiler to establish causality: "optimizing function X will have effect Y," exactly the measurement developers had assumed they were getting all along.

Requirements

Coz, our prototype causal profiler, runs with unmodified Linux executables. Coz requires:

• Python, along with the ggplot package (only required for plotting. See details below)
• Clang 3.1 or newer or another compiler with C++11 support
• Linux version 2.6.32 or newer, including the perf_event API
• libelfin, a C++11 library for accessing ELF binaries and reading DWARF debugging information

On debian or ubuntu, you can install all build dependencies with the following lines:

sudo apt-get install clang
git clone git://github.com/ccurtsinger/libelfin
cd libelfin
make
sudo make install

Building

To build Coz, just clone this repository and run make.

Using Coz

Before running your program with Coz, you will need to identify one or more progress points. These are points in your program that you would like to happen more frequently. For example, in the pbzip2 program under benchmarks/pbzip2 we have inserted a progress point after the code that compresses a block of data.

To add a progress point, add the CAUSAL_PROGRESS macro to the line you would like to execute more frequently. This macro is defined in include/causal.h.

To run a program with Coz, just type coz run --- <your program and arguments> on the command line. You can specify profiling options befor the ---. Run coz run -h for a description of the available options. Profiling output is placed in the file profile.coz by default.

Processing Results

To plot the results from a causal profile, run coz plot. This will generate an image from the profile.coz file in the current directory. This functionality requires the Python ggplot package. You can install this package with the command pip install ggplot.

If you do not have ggplot installed, you can generate a CSV from the causal profile results using the coz process command. The output file profile.csv can be used with most spreadsheet programs.

License

All source code is licensed under the GPLv2 unless otherwise indicated. Copyright (C) 2014 University of Massachusetts Amherst