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lonewolff

Do global variables slow down performance?

7 posts in this topic

Hi Guys,

 

I am just making a renderer in directx for my game.

 

Initially my code was all inlined for testing purposes and I was getting a framerate of ~6000 FPS (Not practical I know).

 

But now I have started cleaning up my code and placing it all into appropriate functions.

 

For ease of use I made the D3DDevice global amongst half a dozen other things and now the framerate has dropped to only ~500 FPS.

 

I have stripped everything out of the main loop (and render loop) and only left my framerate counter (same as I used earlier) and I still get the reduced framerate. I have built in release mode, using the release DLL's.

 

But the only thing I can think of now is that the refernece to the global variables.

 

Is it possible that the globals are slowing things down?

 

Thanks in advance :)

 

Note: I will lock the framerate to 60 FPS when I have my framework sorted out, but I still want the logic to run as fast as possible.

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Thanks for the reply.

 

But, in this case the draw calls are identical to what I started with - A single draw_text function.

 

The only thing that has changed is that I am now wrapping code into functions etc.

 

So, I have lost 90% by just cleaning up the code?

 

BTW, I just checked in debug mode and debug gives me 20 FPS faster than release. I am only using release DLL's too.

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But frametime is the inverse of framerate. And I am sampling over a 1 second period, so it should average out pretty much spot on.

 

Anyway, I just traced the issue. I had wrapped up too much of my draw text function, so it was being created, drawn, and destroyed on every loop.

 

6000 FPS has returned :)

 

So, where one person says 'dont worry about it', I have found a fundamental flaw in my code.  ;)

 

I fully understand that once you start adding game assets, the framerate will drop off in an exponential fashion and should settle around a few hundred FPS (as your link also points out).

 

Thanks again for your help though :)

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Whatever way you want to look at it 1.8 milliseconds is a massive loss when we are talking about a CPU that can handle up to 3500000000 instructions per second / per core.

 

So yes - 'Big loss'.

 

Anyway as I said I found the source of the problem. So yes - the 'Big loss' was an unneccesary one.

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Yeah, fps look nice but it doesn't a good thing to measure performance! Use time is your choice!
Spiro is absolutely right :) and about speed, i did notice some spdeed down in calling function. For examle if u call a const function many times, if inside this func, u call another function (very simle that can be place inside the const function) then suddenly the speed go down !
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