Profiling an application

This readme is a step by step application for using VTUNE to profile a node.

General Overview

In order to profile your application, you will need to do the following:

1. Edit the application CMakeLists.txt to compile it correctly for profiling
2. Edit the application to add any user instrumentation
3. Edit the application launch file in order to launch it under the profiler with desired profile type
4. Edit the launch point of the application to set the timeouts longer
5. Set the correct settings in the pc to allow user profiling
6. Run the node
7. View the profiler results with the VTune GUI

We will go through these step by step here.

CMakeLists.txt

There are a few changes for your application binary that allow it to be profiled.

#  README: This is an example CMakeLists.txt for adding a target that you intend to profile. It
#  is a mix of the regular catkin for ros stuff as well as the extra stuff you need for the 
#  actual profiling bit. Each bit will be explained below.

# Regular ROS stuff, as required for all ros nodes.
cmake_minimum_required(VERSION 3.2)
project(profiler_example)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED YES)

find_package(catkin REQUIRED COMPONENTS
  roscpp
)

find_package(Threads REQUIRED)  # Threads may or may not be required. For the profiler, the target that you link against  
                                # will need to be linked against threads if it uses threads. For basically any ros node
                                # this will be the case because of subscription queues etc. 


catkin_package()

set(THREADS_PREFER_PTHREAD_FLAG ON) # This is just for us, we do prefer pthreads on our system, because linux etc. We
                                    # want this to ensure that we use pthreads which are profilable. Very high chance
                                    # we are using them anyway.

add_executable(test_profiler     # We add our executable as per usual, with all the translation units included. 
    thread_profile_example.cpp
)

#  The following 2 lines are very important if you wish to use the user instrumentation API detailed here:
#  https://software.intel.com/content/www/us/en/develop/documentation/vtune-help/top/api-support/instrumentation-and-tracing-technology-apis/instrumentation-and-tracing-technology-api-reference.html
#  This is so you can include and then link against their libs. For very basic example usage, see the thread_profiling_example.cpp
target_include_directories(test_profiler PRIVATE /opt/intel/oneapi/vtune/latest/sdk/include) 
target_link_directories(test_profiler PRIVATE /opt/intel/oneapi/vtune/latest/sdk/lib64)

# Each of the compiler options and libs we are linking against are quite important, so they will be detailed one at a time. 
target_compile_options(test_profiler PRIVATE
    -g                          # The most important, this compiles your application with profiling symbols.
    -fno-omit-frame-pointer     # This adds some extra information that allows the vtune application to more easily view your profile. 
    -D_LINUX                    # This is suggested by Vtune, i don't know what this does.
    -fno-asm                    # This stops you from ending up with no code trace I think.
)

target_link_libraries(test_profiler PRIVATE 
    ittnotify           # This is important to link against if you are using the user API, see above include directories
    dl                  # This allows the dynamic linking of the user api.
    pthread             # This or the below must be linked if you are using ...