Question

I have never done profiling. Yesterday I programmed a ProfilingTimer class with a static timetable (a map<std::string, long long>) for time storage.

The constructor stores the starting tick, and the destructor calulates the elapsed time and adds it to the map:

ProfilingTimer::ProfilingTimer(std::string name)
 : mLocalNameLength(name.length())
{
 sNestedName += name;
 sNestedName += " > ";

 mStartTick = Platform::GetTimerTicks();
}

ProfilingTimer::~ProfilingTimer()
{
 long long totalTicks = Platform::GetTimerTicks() - mStartTick;

 sTimetable[sNestedName] += totalTicks;

 sNestedName.erase(sNestedName.length() - mLocalNameLength - 3);
}

In every function (or {block}) that I want to profile i need to add:

ProfilingTimer _ProfilingTimer("identifier");

This Profiling work all fine when I build a release version from Visual C++ 2010 Professional. But when I build as Debug I get a huge fps drop (from 63 down to ~20).

These are the numbers I get when I print my timetable (Debug build):

Update() > Tower::Update > : 2551 ms (84100m%)
Update() > Tower::Update > Tower::Update1 > : 1313 ms (43284m%)
Update() > Tower::Update > Tower::Update1 > Tower::FindNewTarget > : 6 ms (204m%)
Update() > Tower::Update > Tower::Update1 > Tower::HasTargetInRange > : 5 ms (184m%)
Update() > Tower::Update > Tower::Update2 > : 659 ms (21756m%)
Update() > Tower::Update > Tower::Update2 > Tower::HasTargetInRange > : 5 ms (187m%)

Update1 and Update2 times the first and second half respectively of Update. Why doesnt they add up to 84,1 %?

Still this 84% is a huge number – in release build I get this output:

Update() > : 770 ms (1549m%)
Update() > Tower::Update > : 722 ms (1452m%)
Update() > Tower::Update > Tower::FindNewTarget > : 44 ms (89m%)
Update() > Tower::Update > Tower::HasTargetInRange > : 92 ms (187m%)

1,4% instead of 84,1%. That is a huge difference!

Anyone knows why?

EDIT: I guess release is much faster than Debug, but why is this profiling so time consuming? Is std::map the time hogger or am I doing something extremely wrong?

EDIT: Updated the code. The initiation wasn’t needed, and now stores the length of mLocalName instead of the actual string.

Answer 1

There are a couple performance issues with your code.

1. You’re needlessly constructing an std::string in your ProfilingTimer constructor. I would recommend using a const char* as your parameter and using a custom Twine/Rope structure to do your appends.
2. Why does mLocalName even exist? Just refer to name directly.
3. As has been previously mentioned, don’t ever profile in debug mode. It is beyond useless.
4. Maps are actually quite slow in practice. I suggest using a hashtable. Unfortunately, implementations are compiler specific. If you’re using Microsoft’s, I believe they have unordered_map available for your use.

5. Instead of doing sTimetable[sNestedName] = 0;, use the iterator you already retrieved.

   Timetable::iterator loc = sTimetable.find(sNestedName);
   if(loc == sTimetable.end())
       sTimetable[sNestedName] = 0;
   

Addendum: Visual Studio comes with a profiler last I checked. Why not just use that?