Sign in to follow this  

OpenGL Strange timing behavior

Recommended Posts

execute42    129
I am profiling a routine (ProcessTexture) that uses OpenGL to do some image procesing. To get a good idea on the routinies performance, I take the average of several trials:

GLuint64 total = 0;

for (int i = 0; i < 1000; ++i) {
glBeginQuery(GL_TIME_ELAPSED, query);
ProcessTexture(input_texture, output_texture);

GLuint64 t = 0;
glGetQueryObjectui64v(query, GL_QUERY_RESULT, &t);
printf("Trial %d = %f\n", i, double(t)*1.0e-6);
total += t;
// Sleep(2000);
double average_millisec = double(total)/1000*1.e-6;
printf("average = %f\n", average_millisec);

Now, the above works well... except if I uncomment the Sleep() or replace Sleep() with an expensive CPU algorithm. In this case, instead of all trials having similiar timing numbers, what happens is about 10 seconds into it, the timings approximately double. Then after another 5 to 8 seconds the timings double again! (not exactly double, but close). My question is why? Why would anything outside of the glBeginQuery() and glEndQuery() affect the timings? In my example, the timings without the Sleep() is 1.3ms, but with Sleep() the ProcessTexture() takes over 7.0ms. GPU: Nvidia GTX 580, windows 7 64. Edited by execute42

Share this post

Link to post
Share on other sites
execute42    129
Here are my actual tiiming numbers:
Without the Sleep(), I ran 20,000 trials...

trial 1 = 1.50883
trial 2 = 1.28858
trial 3 = 1.32256
trial 4 = 1.29549
.... skip a few .....
trial 19996 = 1.2768
trial 19997 = 1.28842
trial 19998 = 1.2767
trial 19999 = 1.27475
Average preprocessing time (ms): 1.28239

And with the Sleep():
trial 1 = 1.65331
trial 2 = 1.40234
trial 3 = 1.40093
trial 4 = 1.39814
trial 5 = 1.41034
trial 6 = 2.59654
trial 7 = 2.59462
trial 8 = 2.59773
trial 9 = 2.60067
trial 10 = 7.92922
trial 11 = 7.88902
trial 12 = 7.56467
trial 13 = 7.57318
trial 14 = 7.5655
trial 15 = 7.492
trial 16 = 7.4943
trial 17 = 7.50099
trial 18 = 7.49405
trial 19 = 7.50326
Average preprocessing time (ms): 4.92952

Is one explanation for this behavior that since that due to somewhat of an incorrect usage of the OpenGLdriver or operating system are adding a bunch of latency?

Share this post

Link to post
Share on other sites
Aks9    1499
No, the reason is changing performance states. Having low GPU load reduces performance state.

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Similar Content

    • By povilaslt2
      Hello. I'm Programmer who is in search of 2D game project who preferably uses OpenGL and C++. You can see my projects in GitHub. Project genre doesn't matter (except MMO's :D).
    • By ZeldaFan555
      Hello, My name is Matt. I am a programmer. I mostly use Java, but can use C++ and various other languages. I'm looking for someone to partner up with for random projects, preferably using OpenGL, though I'd be open to just about anything. If you're interested you can contact me on Skype or on here, thank you!
      Skype: Mangodoor408
    • By tyhender
      Hello, my name is Mark. I'm hobby programmer. 
      So recently,I thought that it's good idea to find people to create a full 3D engine. I'm looking for people experienced in scripting 3D shaders and implementing physics into engine(game)(we are going to use the React physics engine). 
      And,ye,no money =D I'm just looking for hobbyists that will be proud of their work. If engine(or game) will have financial succes,well,then maybe =D
      Sorry for late replies.
      I mostly give more information when people PM me,but this post is REALLY short,even for me =D
      So here's few more points:
      Engine will use openGL and SDL for graphics. It will use React3D physics library for physics simulation. Engine(most probably,atleast for the first part) won't have graphical fron-end,it will be a framework . I think final engine should be enough to set up an FPS in a couple of minutes. A bit about my self:
      I've been programming for 7 years total. I learned very slowly it as "secondary interesting thing" for like 3 years, but then began to script more seriously.  My primary language is C++,which we are going to use for the engine. Yes,I did 3D graphics with physics simulation before. No, my portfolio isn't very impressive. I'm working on that No,I wasn't employed officially. If anybody need to know more PM me. 
    • By Zaphyk
      I am developing my engine using the OpenGL 3.3 compatibility profile. It runs as expected on my NVIDIA card and on my Intel Card however when I tried it on an AMD setup it ran 3 times worse than on the other setups. Could this be a AMD driver thing or is this probably a problem with my OGL code? Could a different code standard create such bad performance?
    • By Kjell Andersson
      I'm trying to get some legacy OpenGL code to run with a shader pipeline,
      The legacy code uses glVertexPointer(), glColorPointer(), glNormalPointer() and glTexCoordPointer() to supply the vertex information.
      I know that it should be using setVertexAttribPointer() etc to clearly define the layout but that is not an option right now since the legacy code can't be modified to that extent.
      I've got a version 330 vertex shader to somewhat work:
      #version 330 uniform mat4 osg_ModelViewProjectionMatrix; uniform mat4 osg_ModelViewMatrix; layout(location = 0) in vec4 Vertex; layout(location = 2) in vec4 Normal; // Velocity layout(location = 3) in vec3 TexCoord; // TODO: is this the right layout location? out VertexData { vec4 color; vec3 velocity; float size; } VertexOut; void main(void) { vec4 p0 = Vertex; vec4 p1 = Vertex + vec4(Normal.x, Normal.y, Normal.z, 0.0f); vec3 velocity = (osg_ModelViewProjectionMatrix * p1 - osg_ModelViewProjectionMatrix * p0).xyz; VertexOut.velocity = velocity; VertexOut.size = TexCoord.y; gl_Position = osg_ModelViewMatrix * Vertex; } What works is the Vertex and Normal information that the legacy C++ OpenGL code seem to provide in layout location 0 and 2. This is fine.
      What I'm not getting to work is the TexCoord information that is supplied by a glTexCoordPointer() call in C++.
      What layout location is the old standard pipeline using for glTexCoordPointer()? Or is this undefined?
      Side note: I'm trying to get an OpenSceneGraph 3.4.0 particle system to use custom vertex, geometry and fragment shaders for rendering the particles.
  • Popular Now