Issue with Thread.SetAffinity and Threading via XNA on the Xbox 360

Question

So I developed a very efficient collision detection system, but the problem is that it still cannot run on the main thread since it's too damn slow.

I tried setting up some threading, and if the thread ends, another thread is created.

if (doneCollisions)
            {
                PopulateGrid();
            }


            if (doneCollisions)
            {
                Thread thread = new Thread(new ThreadStart(CheckCollisionsGrid));

                thread.Start();

            }

void CheckCollisionsGrid()
{
Thread.CurrentThread.SetProcessorAffinity(3);
            doneCollisions = false;
            //Increments through all the grids.
.
.
.
doneCollisions = true;
}

Now I noticed some odd behaviour when debugging. When I called Thread.SetAffinity, it sort of jumped back to it over and over once or twice before finally starting to actually check the collisions.

And now my collisions are delayed by 5-10 seconds...

If anyone has insight please input some here.

imho, the affinity is such low, that the scheduler will "try to begin the action" but reverts that, because there are "better things to do" (wich a higher affinity)... only after 5-10seconds the scheduler finds a slot for your action... — TheHe, Aug 26 '12 at 03:28
@TheHe I thought SetAffinity set's which core to use? What do you suggest to improve my threading? If I just create a new thread it lags, because 2 threads on 1 core isn't that nice. — , Aug 26 '12 at 03:59
aah.. 4sure you're right... i was @ priorities and something.. first: does the xbox have 4 processors?! second: check this -> http://msdn.microsoft.com/en-us/library/windows/desktop/ms684251(v=vs.85).aspx third: set the thread-priority lower? — TheHe, Aug 26 '12 at 05:07
The Xbox only has 3 cores, and one of them (0, if my memory doesn't fail) is reserved for the console's OS, so setting affinity to 3 (fourth processor) would be useless. I'm not sure that's the problem, but try setting it to 1 or 2, or reading documentation regarding such stuff. — Elideb, Aug 27 '12 at 07:46

score 1 · Accepted Answer · answered Sep 05 '12 at 01:44

1

The XBOX 360 has 3 cores with 2 hardware threads per core, producing a total of 6 hardware threads. Threads 0 and 2 are reserved by the XNA Framework, leaving 1, 3, 4 and 5 for you to use.

As for the question, why are you creating a new thread after checking for collisions, to do exactly the same all over again? If you need to repeat the collision checking in a thread, simply put it inside a while(true) loop to keep it going.

answered Sep 05 '12 at 01:44

Tom Lint

483
5
13

Well, I did do exactly what you said, except without the while(true) loop, which is silly. – Sep 05 '12 at 02:40
1

Not exactly silly. Creating & tearing-down threads is an expensive operation. Use an endless loop (I prefer for(;;)) and some synchronization primitives. – Simon Sep 05 '12 at 02:42

Issue with Thread.SetAffinity and Threading via XNA on the Xbox 360

1 Answers1