Profiling a compositing window manager - glXSwapBuffers performance

OpenGL
1

I examine a Compiz performance when it draws desktops using expo plugin. VSync in Compiz and nvidia-settings is disabled ( I run glxgears to test if vsync is disabled). In Compiz I measure a time this way:


paint()
{   
   //get time
   //all opengl commands
   glFlush();
   glFinish();
   //get time
   //calculate paint time

   //get time
   glXSwapBuffers (mDpy, mOutput);
   glFlush();
   glFinish();
   //get time
   //calculate sync/swap time
}

When I run 4 opengl windows I get from Compiz following times:

  • average frame paint time: 29 ms
  • average frame sync/swap time: 28 ms

Those OpenGL windows have internal render speed about 38 fps. Why glXSwapBuffers in Compiz is so slow ?
How to explain that ?

2

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