[Mesa-dev] Performance glxSwapBuffers 32 bit vs. 64 bit

[Michel Dänzer]

On Fre, 2011-11-04 at 13:38 +0100, Theiss, Ingo wrote:
> 
> I am using VirtualGL (http://www.virtualgl.org) for full 3D hardware
> accelerated remote OpenGL applications with latest mesa from git
> (compiled for both 32 bit and 64 bit) on my 64 bit Debian Wheezy box.
> 
> When I run a 32 bit application with VirtualGL I suffer nearly 50%
> performance drop compared when running the same 64 bit application
> with virtualGL. In the first place I have contacted the VirtualGL
> developer and he said that the performance drop is not a VirtualGL
> problem but related to the underlying 3D driver. The performance drop
> seems related to the function glxSwapBuffers which can be seen in the
> function call tracing of VirtualGL:
> 
> 64 bit application with VirtualGL
> -------------------------------------
> [VGL] glXSwapBuffers (dpy=0x00deb900(:0) drawable=0x00a00002 pbw->getglxdrawable()=0x00800002 ) 28.770924 ms
> [VGL] glDrawBuffer (mode=0x00000405 pbw->_dirty=0 pbw->_rdirty=0 pbw->getglxdrawable()=0x00800002 ) 0.005960 ms
> [VGL] glViewport (x=0 y=0 width=1240 height=900 ) 0.003099 ms
> [VGL] glDrawBuffer (mode=0x00000405 pbw->_dirty=0 pbw->_rdirty=0 pbw->getglxdrawable()=0x00800002 ) 0.002861 ms
> [VGL] glPopAttrib (pbw->_dirty=0 pbw->_rdirty=0 pbw->getglxdrawable()=0x00800002 ) 0.002861 ms
> [VGL] glPopAttrib (pbw->_dirty=0 pbw->_rdirty=0 pbw->getglxdrawable()=0x00800002 ) 0.000000 ms
> [VGL] glPopAttrib (pbw->_dirty=0 pbw->_rdirty=0 pbw->getglxdrawable()=0x00800002 ) 0.000954 ms
> [VGL] glXSwapBuffers (dpy=0x00deb900(:0) drawable=0x00a00002 pbw->getglxdrawable()=0x00800002 ) 29.365063 ms
> [VGL] glDrawBuffer (mode=0x00000405 pbw->_dirty=0 pbw->_rdirty=0 pbw->getglxdrawable()=0x00800002 ) 0.006914 ms
> 
> 32 bit application with VirtualGL
> -------------------------------------
> [VGL] glXSwapBuffers (dpy=0x087f7458(:0.0) drawable=0x00a00002 pbw->getglxdrawable()=0x00800002 ) 65.419075 ms
> [VGL] glDrawBuffer (mode=0x00000405 pbw->_dirty=0 pbw->_rdirty=0 pbw->getglxdrawable()=0x00800002 ) 0.005930 ms
> [VGL] glViewport (x=0 y=0 width=1240 height=900 ) 0.003049 ms
> [VGL] glDrawBuffer (mode=0x00000405 pbw->_dirty=0 pbw->_rdirty=0 pbw->getglxdrawable()=0x00800002 ) 0.002989 ms
> [VGL] glPopAttrib (pbw->_dirty=0 pbw->_rdirty=0 pbw->getglxdrawable()=0x00800002 ) 0.004064 ms
> [VGL] glPopAttrib (pbw->_dirty=0 pbw->_rdirty=0 pbw->getglxdrawable()=0x00800002 ) 0.001051 ms
> [VGL] glPopAttrib (pbw->_dirty=0 pbw->_rdirty=0 pbw->getglxdrawable()=0x00800002 ) 0.001044 ms
> [VGL] glXSwapBuffers (dpy=0x087f7458(:0.0) drawable=0x00a00002 pbw->getglxdrawable()=0x00800002 ) 65.005891 ms
> [VGL] glDrawBuffer (mode=0x00000405 pbw->_dirty=0 pbw->_rdirty=0 pbw->getglxdrawable()=0x00800002 ) 0.004926 ms
> 
> 
> Is this performance drop a normal or expected behaviour when running a
> 32 bit application on 64 bit OS or some kind of "bug"?

Probably the latter. You should try to find out where the time is spent
inside glXSwapBuffers in both cases. If the function is (at least
roughly) CPU bound, this should be relatively easy with a profiler such
as sysprof, perf or oprofile. 


-- 
Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer