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pigeon768
l33t
Joined: 02 Jan 2006
Posts: 683
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 Posted: Tue Jan 22, 2013 4:04 pm Post subject: OpenGL unsteady framerate. |
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So I'm trying to learn OpenGL and I hit an issue with every third frame taking significantly longer to render. After cutting down and cutting down and cutting down I finally came to the conclusion that it's simply overhead: but that's an unreasonable conclusion. | Code: | $ cat test.c
#define GL_GLEXT_PROTOTYPES
#include <GL/gl.h>
#include <GL/glext.h>
#include <GL/glut.h>
#include <stdio.h>
#define BUFFER_SIZE 64
static int t;
static int count = 0;
static unsigned char diffs[BUFFER_SIZE];
void readout() {
int i,fps;
for(i = 0;i<BUFFER_SIZE;i++) {
if(diffs[i])
fps=1000/diffs[i];
else
fps=9999999;
printf("%8dfps %8ums/frame\n",fps,diffs[i]);
}
exit(0);
}
void display() {
const GLuint now = glutGet(GLUT_ELAPSED_TIME);
if(now > 1000) {
diffs[count++] = now - t;
if(count==BUFFER_SIZE) readout();
}
t = now;
glClear(GL_COLOR_BUFFER_BIT);
glClearColor(0.0f,0.0f,0.0f,0.0f);
glutSwapBuffers();
glutPostRedisplay();
}
int main(int argc, char **argv) {
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_RGBA|GLUT_DOUBLE);
glutInitWindowSize(640,480);
glutCreateWindow("test");
printf("OpenGL version: %s\n",glGetString(GL_VERSION));
glutDisplayFunc(display);
t = glutGet(GLUT_ELAPSED_TIME);
glutMainLoop();
return 0;
} |
As you can see, it does nothing -- just clears the buffer and shovels it onto the display. | Code: | $ gcc -lglut test.c -march=native -O3 -o test && ./test
OpenGL version: 3.0 Mesa 9.0.1
35fps 28ms/frame
250fps 4ms/frame
30fps 33ms/frame
1000fps 1ms/frame
1000fps 1ms/frame
62fps 16ms/frame
66fps 15ms/frame
30fps 33ms/frame
500fps 2ms/frame
1000fps 1ms/frame
32fps 31ms/frame
1000fps 1ms/frame
1000fps 1ms/frame
32fps 31ms/frame
1000fps 1ms/frame
333fps 3ms/frame
50fps 20ms/frame
100fps 10ms/frame
58fps 17ms/frame
62fps 16ms/frame
30fps 33ms/frame
500fps 2ms/frame
1000fps 1ms/frame
47fps 21ms/frame
100fps 10ms/frame
58fps 17ms/frame
58fps 17ms/frame
30fps 33ms/frame
1000fps 1ms/frame
1000fps 1ms/frame
32fps 31ms/frame
1000fps 1ms/frame
1000fps 1ms/frame
41fps 24ms/frame
125fps 8ms/frame
30fps 33ms/frame
1000fps 1ms/frame
1000fps 1ms/frame
66fps 15ms/frame
58fps 17ms/frame
30fps 33ms/frame
1000fps 1ms/frame
1000fps 1ms/frame
32fps 31ms/frame
1000fps 1ms/frame
1000fps 1ms/frame
47fps 21ms/frame
100fps 10ms/frame
29fps 34ms/frame
1000fps 1ms/frame
1000fps 1ms/frame
20fps 48ms/frame
1000fps 1ms/frame
1000fps 1ms/frame
32fps 31ms/frame
1000fps 1ms/frame
30fps 33ms/frame
500fps 2ms/frame
333fps 3ms/frame
35fps 28ms/frame
58fps 17ms/frame
1000fps 1ms/frame
31fps 32ms/frame
1000fps 1ms/frame |
So most frames take ~1ms to render, some take significantly longer. There's not a whole lot of CPU usage going on during this time.
What gives? Video card is intel HD4000, drivers are up to date and all that. It plays eg Trine 2 smoothly, so i know the video drivers can't be that dorked up.
If I comment out the glClear() and glClearColor() I get the same problem. With glutSwapBuffers() commented I get 0ms per frame, but that's obviously not the solution. |
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eccerr0r
Watchman
Joined: 01 Jul 2004
Posts: 9677
Location: almost Mile High in the USA
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| Posted: Wed Jan 23, 2013 1:04 am Post subject: |
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I wish I knew more about graphics programming and hardware so all I can do is compile and run the program :)
On my G965 machine (also Intel Graphics) it seems to be a very consistent 16-17ms per frame (OpenGL 2.1/Mesa 9). So this is weird. I recently fried both my HD3000 and HD4000 machines (due to the udev thing) so I can't test them at the moment...
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pigeon768
l33t
Joined: 02 Jan 2006
Posts: 683
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| Posted: Wed Jan 23, 2013 4:53 am Post subject: |
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Well hmm. I was able to make it go away and get a steady 16/17ms per frame by disabling "TearFree" in /etc/X11/xorg.conf.d/50-intel.conf. Of course, now I have tearing.  I think I'm going to keep TearFree disabled at least for now. There are other ways to get rid of tearing with video playback.
(note: 16.666ms is the magic number because that's the time between frames on a 60Hz monitor) |
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eccerr0r
Watchman
Joined: 01 Jul 2004
Posts: 9677
Location: almost Mile High in the USA
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| Posted: Wed Jan 23, 2013 5:50 am Post subject: |
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Curious - what hardware do you have that needs tearfree? I've yet to run across hardware that needed tearfree, or I can't tell the difference looking at it. My HD3000 is a LCD analog monitor, my HD4000 is a LVDS laptop display, and the G965 is also analog...
hmm...hope this kernel works... Can't believe I broke so many machines with this udev thing...
Addition: I got my HD3000 and HD4000 working again, no tearfree, stable 13-14 and 16-17 ms/frame, respectively.
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pigeon768
l33t
Joined: 02 Jan 2006
Posts: 683
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| Posted: Wed Jan 23, 2013 10:58 am Post subject: |
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CPU is a i5-3320M, video card is HD4000.
It doesn't strictly need it, but I get enough tearing that I can't not notice it. It's the sort of thing you might never notice until someone points it out to you, and then it bugs the hell out of you, you know? |
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eccerr0r
Watchman
Joined: 01 Jul 2004
Posts: 9677
Location: almost Mile High in the USA
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| Posted: Wed Jan 23, 2013 6:42 pm Post subject: |
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The test platforms I have are an i5-3317U (HD4000) - LVDS laptop display, and an i7-2700K (HD3000) - actually it's HDMI to DVI LCD interface. The HD3000 is actually refreshing at 75FPS hence the higher frame rate. The G965 (Core2Duo) is hooked up via analog to a DLP display.
I will need someone to point out the tearing, I don't even notice it on any of my displays... I had a contrived test at one point that I notice some "tearing" but not sure if it's the same thing...
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Mad Merlin
Veteran
Joined: 09 May 2005
Posts: 1155
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| Posted: Wed Jan 23, 2013 7:11 pm Post subject: |
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I get mostly 0ms/frame with a small number of 1ms/frame, video card is a GTX 670:
| Code: |
OpenGL version: 4.2.0 NVIDIA 304.37
1000fps 1ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
1000fps 1ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
9999999fps 0ms/frame
1000fps 1ms/frame
9999999fps 0ms/frame
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I might suggest using SDL instead of GLUT, GLUT is... not very sophisticated and yet doesn't manage to be much easier (if at all) to use than SDL.
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eccerr0r
Watchman
Joined: 01 Jul 2004
Posts: 9677
Location: almost Mile High in the USA
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| Posted: Thu Jan 24, 2013 5:03 pm Post subject: |
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Anyone happen to know how to stop xorg/opengl from using the monitor refresh rate as the limit to how fast it draws screens? Seems some drivers limit to refresh rate and some just blasts it out as fast as it can to the video buffer...
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Mad Merlin
Veteran
Joined: 09 May 2005
Posts: 1155
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| Posted: Thu Jan 24, 2013 8:12 pm Post subject: |
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| eccerr0r wrote: | | Anyone happen to know how to stop xorg/opengl from using the monitor refresh rate as the limit to how fast it draws screens? Seems some drivers limit to refresh rate and some just blasts it out as fast as it can to the video buffer... |
That would be vsync. I believe all drivers have a way to toggle it (which is different from every other video driver) and most default to vsync on. For the Nvidia blob, it's an option in nvidia-settings, for radeon, it seems to be SwapbuffersWait or possibly EnablePageFlip in xorg.conf, not sure about the others.
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Jean-Paul
Guru
Joined: 13 Apr 2009
Posts: 307
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| Posted: Thu Jan 24, 2013 8:59 pm Post subject: |
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for intel I use
| Quote: | Section "Device"
Identifier "Intel HD4000"
Driver "intel"
Option "AccelMethod" "sna"
Option "SwapbuffersWait" "false"
EndSection |
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eccerr0r
Watchman
Joined: 01 Jul 2004
Posts: 9677
Location: almost Mile High in the USA
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| Posted: Fri Jan 25, 2013 5:13 am Post subject: |
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Ah... I wish the option was the same for all drivers, and documented... That has to be one of the most obscure options...
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