Hi Rick, The way that OpenGL drivers work is that there is an OpenGL FIFO per graphics context, your application fills the FIFO with data and OpenGL tokens, and then the driver sucks the tail of the FIFO in batches and fires it off GPU. This fifo decouples the application thread from the GPU, so in effect the CPU and the GPU can largely work in a parallel.
However, if OpenGL FIFO fills up because the rate at which you are pushing data into it exceeds the rate at which it's been emptied then the application thread will stall and the draw dispatch times will go up. Sometimes you can see some rather no linear draw dispatch times due to small changes in load on the GPU suddenly causing the app to stall. Even when this happens there is still a bit of leeway before you start dropping frames. Another reason for seeing large draw dispatch times is the presence of OpenGL operations that require getting data back from OpenGL (such glGet or glReadPixels), because this forces OpenGL to push all the data ahead of it down to the GPU, read back the result and then finally get this back to application thread. This roundtrip is very expensive and should be avoided where possible. Robert. On Thu, Mar 18, 2010 at 3:18 PM, Rick Appleton <rick.apple...@altenpts.nl> wrote: > Hi everyone, > > We were just doing some performance testing when we noticed that increasing > the image quality in the NVidia control panel (adding anisotropic filtering, > anti-aliasing and multi-sampling) makes the time spent in the 'Draw' section > increase greatly. This wasn't something we were expecting. The time in GPU > also goes up, but that is to be expected. > > We're assuming the extra time is spent in the driver somewhere, but we have > no clue why. > > Would anyone dare to hazard a guess? > > Thank you! > > Cheers, > Rick > > ------------------ > Read this topic online here: > http://forum.openscenegraph.org/viewtopic.php?p=25798#25798 > > > > > > _______________________________________________ > osg-users mailing list > osg-users@lists.openscenegraph.org > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
