ProfilingWesnoth

From The Battle for Wesnoth Wiki

Linux

When using either scons or cmake to build, there are four options available for profiling which are listed below. For cmake use -DPROFILER=<name>, for scons use profiler=<name>.

gperftools

To use gperftools:

  1. Install the packages google-perftools (needed later for running google-pprof) and libgoogle-perftools-dev (needed in order to use the -lprofiler linker option).
  2. In a terminal, export the CPUPROFILE variable, such as export CPUPROFILE=./wesnoth-prof.
  3. Build any executable while setting either -DPROFILER=gperftools (cmake) or profiler=gperftools (scons).
  4. Run the executable and have it do any task(s) as needed to get relevant profiling information.
  5. Generate the human-readable profiling output using the command google-pprof <executable> <profiling info> > prof.txt for a text file, or google-pprof -gif <executable> <profiling info> > prof.gif for a viewable gif image.

Unfortunately, the output, whether graphical or text, doesn't provide any labels for what the values mean. For the text output, the columns are:

  1. The number of profiling samples in this function
  2. The percentage of profiling samples in this function
  3. The percentage of profiling samples in the functions printed so far
  4. The number of profiling samples in this function and its callees
  5. The percentage of profiling samples in this function and its callees
  6. The function name

For the graphical output, each square will contain:

  1. The namespace/class/method profiled, each of those on a separate line
  2. The number of profiling samples in this function
  3. The percentage of profiling samples in this function (in parenthesis)
  4. The number of profiling samples in this function and its callees
  5. The percentage of profiling samples in this function and its callees (in parenthesis)

perf

To use perf:

  1. Install the packages linux-tools-common and linux-tools-<kernel version>, ie linux-tools-5.8.0-55-generic.
  2. Run perf record <executable>. To do this you will need to either:
    1. Run the executable as root
    2. Switch to root and run echo 2 > /proc/sys/kernel/perf_event_paranoid
    3. Create a new group that has rights to use perf and add your user to it, ie:

cd /usr/bin

groupadd perf_users

chgrp perf_users perf

chmod o-rwx perf

setcap cap_sys_admin,cap_sys_ptrace,cap_syslog=ep perf


Once that's complete, there will be a perf.data file created, and commands like perf report can be run.

gcov

To use gcov:

  1. After the executable is built and been executed as needed, there will be many .gcda and .gcno files in the source directory.
  2. Generate the human readable information from those files with gcov ./**/*.gcno. This will generate a .gcov file for each source file.
  3. Open any gcov file(s) of interest.

gprof

To use gprof:

  1. After the executable is built and been executed as needed, there will be a gmon.out file generated.
  2. Execute gprof <executable> gmon.out > prof.txt. This may take quite a while and create a rather large file.
  3. Open prof.txt.

Profile Guided Optimization (PGO)

Profile guided optimization is, to summarize it extremely briefly, a way to let the compiler generate a higher performing executable by providing it additional information (aka a profile) about how the program is used. While there is support for enabling this in scons and cmake, no executables are currently built using this for two reasons:

  1. It is much more work.
    1. The executable must be built first with the additional instrumentation needed to generate the profiling data.
    2. That executable must then be run and perform tasks that accurately mimic real world use. If your profile contains information primarily on unimportant and rarely executed tasks, or if the way the tasks are executed don't match what happens in the real world, then the profile generated will be used by the compiler to make optimizations that have no impact on the program's performance or may even make it slower.
    3. The executable must then be built a second time, this time using the information gathered in the profile to help direct how optimizations are done.
  2. For the wesnoth client (wesnoth.exe) for example, there's no set of cases defining what situations would need to be run to generate a good profile. For the server executables (such as wesnothd), while it would be fairly easy to generate a good profile by simply letting an instrumented build run for a day or so, there is currently no need to do this since they're already able to perform adequately without any optimizations being enabled at all.

To use PGO for cmake:

  1. Set -DPGO_DATA=generate and build the executable
  2. Run the executable to generate the profile information, which will be saved to the pgo_data/ directory (if using GCC) or a .profraw file if using Clang.
  3. Set -DPGO_DATA=use and build the executable again

To use PGO for scons:

  1. Set -DPGO_DATA=generate and build the executable
  2. Run the executable to generate the profile information, which will be saved to the pgo_data/ directory (if using GCC) or a .profraw file if using Clang.
  3. Set -DPGO_DATA=use and build the executable again
This page was last edited on 9 June 2021, at 21:13.