Valgrind

Description

The Valgrind tool suite provides a number of debugging and profiling tools that help you make your programs faster and more correct. The most popular of these tools is called Memcheck. It can detect many memory-related errors that are common in C and C++ programs and that can lead to crashes and unpredictable behaviour.

Using Valgrind on Hopper

Prepare Your Program

Compile your program with -g to include debugging information so that Memcheck's error messages include exact line numbers. Using -O0 is also a good idea, if you can tolerate the slowdown. With -O1 line numbers in error messages can be inaccurate, although generally speaking running Memcheck on code compiled at -O1 works fairly well, and the speed improvement compared to running -O0 is quite significant. Use of -O2 and above is not recommended as Memcheck occasionally reports uninitialised-value errors which don't really exist.

Load Module

 module load valgrind

Running Serial Programs

If you normally run your program like this:

myprog arg1 arg2

Use this command line:

valgrind --leak-check=yes myprog arg1 arg2

Memcheck is the default tool. The --leak-check option turns on the detailed memory leak detector.

Your program will run much slower (eg. 20 to 30 times) than normal, and use a lot more memory. Memcheck will issue messages about memory errors and leaks that it detects.

Running Parallel Programs Interactively

Get an interactive terminal (sample command below), detailed directions here.

qsub -I -V -q interactive -l mppwidth=24 -l walltime=00:30:00

If you are running your program like this:

aprun -n 24 ./myprog arg1 arg2

Simply add valgrind to your command (after aprun).

module load valgrind
aprun -n 24 valgrind --leak-check=yes ./myprog arg1 arg2

Running Parallel Programs in Batch

In your batch script, simply 1. load the module; 2. add "valgrind" in front of your command. For example, your aprun line will be replace by the following:

module load valgrind
aprun -n 24 valgrind --leak-check=yes ./myprog arg1 arg2

Link to Outside Documentation

This page is based on the "Valgrind Quick Start Page". For more information about valgrind, please refer to http://valgrind.org/

For questions on using Valgrind at NERSC contact the consultants at consult@nersc.gov.

Availibility