Slow OpenGL context access on Ubuntu 12.4 - linux

Question

I have an application which accesses OpenGL context.I run it on 2 OSs :
1.Kubuntu 13.4
2.Ubuntu 12.4
I am experiencing the following issue: on OS 1 it takes around 60 ms to setup the context, while on OS 2 it takes 10 times more.Both OSs use Nvidia GPUs with driver version 319.It also seems like OpenGL API calls are slower in general for OS 2.The contexts are offscreen.Currently I have no clue what could cause it.My question is what are possible sources of such an overhead?X11 setup?Or may be something on the OS level?
Another difference is that OS 1 uses Nvidia GTX680 while OS2 uses Nvidia GRID K1 card.Also OS2 resides on a server and the latency tests are run locally on that machine.
UPDATE:
This is the part which causes most of overhead:
typedef GLXContext (*glXCreateContextAttribsARBProc)(Display*, GLXFBConfig, GLXContext, Bool, const int*);
typedef Bool (*glXMakeContextCurrentARBProc)(Display*, GLXDrawable, GLXDrawable, GLXContext);
static glXCreateContextAttribsARBProc glXCreateContextAttribsARB = 0;
static glXMakeContextCurrentARBProc glXMakeContextCurrentARB = 0;
int main(int argc, const char* argv[]){
static int visual_attribs[] = {
None
};
int context_attribs[] = {
GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
GLX_CONTEXT_MINOR_VERSION_ARB, 0,
None
};
Display* dpy = XOpenDisplay(0);
int fbcount = 0;
GLXFBConfig* fbc = NULL;
GLXContext ctx;
GLXPbuffer pbuf;
/* open display */
if ( ! (dpy = XOpenDisplay(0)) ){
fprintf(stderr, "Failed to open display\n");
exit(1);
}
/* get framebuffer configs, any is usable (might want to add proper attribs) */
if ( !(fbc = glXChooseFBConfig(dpy, DefaultScreen(dpy), visual_attribs, &fbcount) ) ){
fprintf(stderr, "Failed to get FBConfig\n");
exit(1);
}
/* get the required extensions */
glXCreateContextAttribsARB = (glXCreateContextAttribsARBProc)glXGetProcAddressARB( (const GLubyte *) "glXCreateContextAttribsARB");
glXMakeContextCurrentARB = (glXMakeContextCurrentARBProc)glXGetProcAddressARB( (const GLubyte *) "glXMakeContextCurrent");
if ( !(glXCreateContextAttribsARB && glXMakeContextCurrentARB) ){
fprintf(stderr, "missing support for GLX_ARB_create_context\n");
XFree(fbc);
exit(1);
}
/* create a context using glXCreateContextAttribsARB */
if ( !( ctx = glXCreateContextAttribsARB(dpy, fbc[0], 0, True, context_attribs)) ){
fprintf(stderr, "Failed to create opengl context\n");
XFree(fbc);
exit(1);
}
/* create temporary pbuffer */
int pbuffer_attribs[] = {
GLX_PBUFFER_WIDTH, 800,
GLX_PBUFFER_HEIGHT, 600,
None
};
pbuf = glXCreatePbuffer(dpy, fbc[0], pbuffer_attribs);
XFree(fbc);
XSync(dpy, False);
/* try to make it the current context */
if ( !glXMakeContextCurrent(dpy, pbuf, pbuf, ctx) ){
/* some drivers does not support context without default framebuffer, so fallback on
* using the default window.
*/
if ( !glXMakeContextCurrent(dpy, DefaultRootWindow(dpy), DefaultRootWindow(dpy), ctx) ){
fprintf(stderr, "failed to make current\n");
exit(1);
}
}
/* try it out */
printf("vendor: %s\n", (const char*)glGetString(GL_VENDOR));
return 0;
}
Specifically , the line :
pbuf = glXCreatePbuffer(dpy, fbc[0], pbuffer_attribs);
where the dummy pbuffer is created is the slowest.If the rest of function calls take in average 2-4 ms,this call takes 40 ms on OS 1. Now , on OS2 (which is slow) the pbuffer creation takes 700ms! I hope now my problems looks more clear.

Answer 1

Are you absolutely sure "OS2" has correctly set up drivers and isn't falling back on SW OpenGL (Mesa) rendering? What framerate does glxgears report on each system?
I note Ubuntu 12.4 was released April 2012 while I believe NVidia's "GRID" tech wasn't even announced until GTC May 2012 and I think cards didn't turn up until 2013 (see relevant Nvidia press releases). Therefore it seems very unlikely Nvidia's drivers as supplied with Ubuntu 12.4 support the grid card (unless you've made some effort to upgrade using more recent driver releases from Nvidia?).
You may be able to check the list of supported hardware in /usr/share/doc/nvidia-glx/README.txt.gz's Appendix A "Supported NVIDIA GPU Products" (at least that's where this useful information lives on my Debian machines).