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Member Since 26 Nov 2012
Offline Last Active Aug 17 2015 08:47 AM

Posts I've Made

In Topic: glSwapBuffers() - odd performance pattern

30 November 2012 - 02:54 AM

Hah! That's interesting... So it doesn't occur if you ensure PE isn't running?

Yep. If I shut it off I can get a stable framerate with up to 15k sprites on the screen, which is well above my target. If I couldn't handle such a measly number without stuttering, I was going going to be in trouble once I turned scripting and audio back on and added the 3D bits.

To build your own GPU-side frame-timer, you basically want to create a ring-buffer of "event"/"query" objects and submit one at the start of each frame
-- e.g. an array of 3 or more queries, and increment a counter (wrapping around to 0 at the top of the array) that selects which one you'll be submitting that frame.
You need more than one query because of the latency between the CPU and GPU.
Before you reuse a event/query, you can read it's actual time value, which hopefully has actually been written by the time your array/ring wraps around.
I've not done this with OpenGL, but I believe you can use the ARB_timer_query extension.
Most of the game engines I've used have had some kind of on-screen display of this timer info , e.g. two bars at the bottom of the screen, one for CPU time in ms and one for GPU time in ms, with lines/markings on the bars showing 16.6 and 33.3ms (60FPS and 30FPS, respectively).

Alright, thanks. I'll look into it later.

In Topic: glSwapBuffers() - odd performance pattern

30 November 2012 - 02:11 AM

I figured it out. Remember I said the lag spikes happened once every second regardless of framerate? Remember also I said I could monitor GPU usage from Process Explorer? Turns out, PE's probing of the GPU was adding a huge amount of delay (up to 15 ms) to a few frames once every second.
I still think it's strange that only OpenGL applications behave like this, though.

Hodgman: What you said about sending work to the GPU faster than it can handle it, how could I determine if this was happening? Not that I think it's happening now, but I would like to be prepared if the need arose. Could you recommend a profiler?

In Topic: glSwapBuffers() - odd performance pattern

27 November 2012 - 02:26 PM

Well, it's an engine, not a specific game, so I don't really have a fixed target performance. Although I admit I am getting sidetracked a bit.

In Topic: glSwapBuffers() - odd performance pattern

26 November 2012 - 09:59 PM

Suppose I inserted an empty loop in the middle of my game loop such that I can be sure that the time spent outside of rendering amounts to over 95% of the run time of the program and the framerate never exceeds 40 fps. What does it mean if the framerate still drops quite visibly?
I can also monitor GPU usage from Process Explorer and it practically idles to run my program.

EDIT: If the answer to the above question is "it doesn't mean anything", is there any way I can improve my code? My target is being able to draw as many sprites as possible as efficiently as possible, considering that they'll be moving constantly and independently, and that sprites may be created or destroyed at any time.

In Topic: glSwapBuffers() - odd performance pattern

26 November 2012 - 09:03 PM

Update: I've determined that the problem doesn't appear to be my code. I observed the exact same performance pattern when I tried running Quake 3 Arena without vsync. Only OpenGL applications have this problem.
Well, now I really don't know what to do. If it's a driver issue, all I can do is hope it gets fixed eventually or try to find an older version that doesn't have this problem.