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code:profiling

Profiling

A collection of code profiling techniques follows.

Dynamic Memory Allocation

Typical problems with dynamic memory management are:

  1. leaks and
  2. corruption.

While the latter is rather tricky to analyse, for memleaks there is valgrind. Invocation as follows:

$ gcc -g test.c
$ valgrind --leak-check=full ./a.out

Performance

When programming, code complexity (O-notation) is the main factor identifying CPU-intense algorithms. Reducing code complexity often doesn't suffice, though. E.g. IO-intense operations often lead to delays at run-time which isn't covered by O-notation, at all. This means that aside of complexity analysis, there always should be run-time code execution time measurement.

GProf

gprof is a profiler integrated into gcc. Enabled at compile-time, the program collects profiling data for later analysis using gprof tool:

$ gcc -pg -g test.c
$ ./a.out
$ gprof a.out gmon.out

Perf

On recent kernels, perf is the best tool for the job. It may profile the whole system like with obsoleted OProfile but may be limited to a single program, also. Before executing the workload to profile (or while it is running), call:

# perf record

When done, finish recording using CTRL-c. perf data will be written to perf.data in local directory. To analyse, call:

# perf report

Python

Profiling Python is pretty simple, using cPython module:

$ python -m cPython myscript.py

Coverage

Code coverage means to have a look at how often each line of code is being executed. Interestingly, this can be used to “measure” the code's complexity. This way a broader view over the problem can be provided, e.g. answering the question if a seldomly executed O(n) algorithm is heavier than an O(log(n)) one being executed all the time. One of the best tools to analyse the code coverage is gcov:

$ gcc -fprofile-arcs -ftest-coverage test.c
$ ./a.out
$ gcov tmp.c

this will create the file test.c.gcov containing the annotated source code of test.c.

If linking happens in a separate step, some additional flags have to be passed to linker:

CFLAGS  += -fprofile-arcs -ftest-coverage
LDFLAGS += -lgcov --coverage
code/profiling.txt · Last modified: 2020/03/29 12:13 (external edit)