[osg-users] Rendering performance issues

Paul Martz pmartz at skew-matrix.com
Mon Jul 7 19:00:26 PDT 2008


The first image (vsyncOFF-1GPU.jpg) shows the timing rendering 1 slave
camera on an extended (2880x900) dual-monitor on a single Nvidia card.  Note
the 211Hz rendering rate with VSync off and the substantial Draw/GPU
overlap.  [Note that in all of these timing tests none of the CPUs appeared
more than 50% loaded.]  This is the type of performance I was anticipating.

Now all I did was turn on Vsync.  The second image (vsyncON-app-long.jpg)
now shows a 60Hz rendering rate as expected (with a delay after GPU waiting
for VSync), but no Draw/GPU overlap, there's even a slight gap between the
two?  Why is this different now? 

I suspect this issue is caused by the graphics card having an upper limit on
the number of buffer swaps queued up. Once the limit of queued swaps is
reached, the card won't start processing the next frame until it performs
the swap for the current frame, thus causing the "gap" that you see. This
is, of course, not an issue with vsync disabled.
 
Not sure about the "gap" in the rest of your post; perhaps Robert has more
info.
 
I hope that helps,
 
Paul Martz
Skew Matrix Software LLC
http://www.skew-matrix.com <http://www.skew-matrix.com/> 
+1 303 859 9466
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