Loop Design - Low CPU Cost

[Rytz]

Hey All,

I've been reading up on loop design for the last couple of days, searching forums and what not. Did some searching on this site to try and find out as much as possible before I start asking around on the forums.

As of right now, I'm using Sleep(1) to keep the CPU cost low on my "tight" loops. I have some GUI loops (for irrLicht) and some loops that use the typical "while (true){}" approach because they are waiting for flag variables to be set.

I'm curious to know what other folks are doing to keep their CPU usage down but still keep their program as efficient as possible. Any info or examples would be appreciated. Are there any cross-platform libs out there that work with handling system resources? I understand that handling system / CPU resources is OS dependent.

Thanks in advance for any info. Sorry if I missed a topic about this in the forum already.

[olivehehe_03]

I haven't had to worry about anything like this in my project yet, but I read about it somewhere a while back and it seemed pretty useful...

Basically, your main loop looks like this, not exactly like this, I know, but bear with me...

Code: Select all

	while(device->run())
	{
		if (device->isWindowActive())
		{
			driver->beginScene(true, true, video::SColor(255,0,0,255));
			doSomething();
			doSomethingElse();
			doSomeOtherStuff();
			smgr->drawAll();
			driver->endScene();
		}
	}

Now as you know, all that is happening every frame, which can sometimes give the CPU alot of things to do. What you can do though is change it around a little so that some things are only happeneing every second or third frame by doing something like this, again it's half C++, half pseudocode so yours would look diferent...

Code: Select all

int framecount = 0;
while(device->run())
	{
		if (device->isWindowActive())
		{
			driver->beginScene(true, true, video::SColor(255,0,0,255));
			framecount++;
			doSomething();
			if (framecount == 2)
			{
				doSomethingElse();
			}
			if (framecount == 3)
			{
				doSomeOtherStuff();
				framecount = 0;
			}
			smgr->drawAll();
			driver->endScene();
		}
	}

I hope thats not too hard to follow, but basically doSomething(); is running every frame, doSomethingElse(); is running every second frame and doSomeOtherStuff(); is running every third frame.

It might not seem like much written here, but think about how you would use it in a game. Less important things (like input and even AI and physics depending on your game) can be made to run every second or third frame, or even less often if you want, whereas more important things can be run every frame to make sure your game runs smoothly.

Well that was quite a post... Hope that helps

[Rytz]

Well that was quite a post... Hope that helps

Thanks a lot for the post and insights.

What you put up there definitely wasn't confusing. Actually, you made me think more about what I'm trying to accomplish with my loops. I was so concerned with just trying to find a way to free up resources that I was missing the real objective: freeing up resources when actions are NOT being performed.

Sleep() is working really good (since I'm on windows - inactive program times are at 0% CPU now) but when I get to porting it over I'm going to have to add some defines for using a *nix based alternative (read some of them already during my research).

Thanks again for your post - it helped out a lot .

[roxaz]

this isnt exactly what you need but it might help i gues http://www.mindcontrol.org/~hplus/graph ... _loop.html

[Luben]

"- Added sleep() methd to IrrlichtDevice, for pausing the Irrlicht process for a longer amount of time."

Changelog for 1.3

[Cocodrilo]

Thanks olivehehe_03, quite usefull nice idea!

[Rytz]

this isnt exactly what you need but it might help i gues http://www.mindcontrol.org/~hplus/graph ... _loop.html

Thanks - it's definitely some good info on loop design. I might have to incorporate something like that later.

"- Added sleep() methd to IrrlichtDevice, for pausing the Irrlicht process for a longer amount of time."

Changelog for 1.3

Well that will definitely help me with portability . I'll be testing that one out tonight.

[Vuen]

I don't know a whole lot about loop design. I just have one loop in which everything happens:

Code: Select all

    ITimer* timer = device->getTimer();
    u32 timelast = timer->getRealTime()-1;
    u32 timenow = timer->getRealTime();

    // Main loop
    while (device->run())
    {
        timenow = timer->getRealTime();
        time = timenow - timelast;
        timelast = timer->getRealTime();

        // Start the scene
        video->beginScene(true, true, SColor(255, 0, 0, 0));

        if (time > 0) {
            control->go(time);
            level->go(time);
        }

        // Draw everything
        scene->drawAll();
        gui->drawAll();

        // End the scene
        video->endScene();
    }

The go(time) tells the various components to do their stuff, and lets them know how much time has passed (so how far a character should be moved, etc.)

[Rytz]

I don't know a whole lot about loop design. I just have one loop in which everything happens:

Code: Select all

    ITimer* timer = device->getTimer();
    u32 timelast = timer->getRealTime()-1;
    u32 timenow = timer->getRealTime();

    // Main loop
    while (device->run())
    {
        timenow = timer->getRealTime();
        time = timenow - timelast;
        timelast = timer->getRealTime();

        // Start the scene
        video->beginScene(true, true, SColor(255, 0, 0, 0));

        if (time > 0) {
            control->go(time);
            level->go(time);
        }

        // Draw everything
        scene->drawAll();
        gui->drawAll();

        // End the scene
        video->endScene();
    }

The go(time) tells the various components to do their stuff, and lets them know how much time has passed (so how far a character should be moved, etc.)

Well, my problem stems from having some network data "queues" in place that need to be continuously checked for new data. If there is no data, the loop basically comes down to "while(true){}" so it's burning a lot of CPU. I don't want the loop itself to be "paused" because I want the queue to be checked as frequently as possible.

[Vuen]

Yeah, you need something in there to make your thread sleep to give the rest of the computer a chance to do stuff. If you're drawing stuff to the screen, Irrlicht will do this automatically; otherwise, as Luden said, just go with Irrlicht's sleep method.

[Rytz]

Thanks everyone for the advice and info .