Valgrind #

Valgrind is an instrumentation framework which supplies several very useful debugging and profiling tools. Among these are the popular memcheck, which thoroughly checks for incorrect memory access, and cachegrind, which profiles the CPU usage of a program. I have found this to be a really well-designed, useful tool to measure the performance of a WARPXM run, without the need to add any custom instrumentation to the code.

How it works #

Valgrind adds instrumentation to any existing executable by intercepting all instructions from the unmodified code and emulating the CPU, adding instrumentation code in the middle. There is no need to modify the existing code to obtain profiling measurements, just run valgrind directly against the executable, for example:

valgrind --tool=callgrind /path/to/target/release/warpxm -i input.inp

Simple as that!

Cachegrind vs. Callgrind #

Callgrind and cachegrind are two Valgrind profiling tools that serve very similar functions. Both attempt to profile the runtime cost of your program, giving you a breakdown of how much “cost” was associated with each function call. The exact meaning of “cost” differs between the tool. The profiling data is written to a file named e.g cachegrind.out.<pid> where <pid> is the process ID of the userspace process.

Cachegrind #

Cachegrind is a profiling tool that is meant to be reproducible. Rather than measuring the execution time of the program, it attempts to measure the exact number of CPU instructions executed by the program.

Callgrind #

Callgrind is a profiling tool that records call history events (data reads, cache misses, etc.) and attributes the cost of each event to the relevant function (and its parents, up the call stack).