perf

# Measuring performance

In general, to obtain useful information from binaries, certain compile flags should be used.

## Perf

For using perf, one should compile OOFEM with the flag -fno-omit-frame-pointer First record a session using

perf record -g ./oofem -f myinputfile.in

which will generate a perf.data file.

Then you can visualize the results in several ways. A good, simple to understand method is to use Gprof2Dot to generate a complete callgraph:

perf script | ./gprof2dot.py -f perf | dot -Tsvg -o output.svg

Or use the ncurses program

perf report -G --sort comm,dso

Perf has very small overhead, but only does statistical sampling.

Users of perf will likely first need to turn off the restrictions before they are able to run perf record as normal users:

sudo sh -c "echo 0 > /proc/sys/kernel/kptr_restrict"

## Callgrind

Callgrind is a tool in valgrind, and should only be used on medium. This has a huge overhead, so expect OOFEM to run over a hundred times slower through valgrind. Simply run

valgrind –tool=callgrind ./oofem -f myinputfile.in

and you will produce a new file named callgrind.out.123456 where the numbers at the end are randomized. Open this file in Kcachegrind to visualize the results.