Hi Folks,
I know this has been discussed several times in the mailing list, but I
could not figure out everything by browsing the archives.
Even knowing that the osgViewer will soon replace the Producer
dependency, I believe my questions are independent on that and remain
the same.
I'm working under WindowsXP, on a workstation with a
- Pentium D dual core
- nVidia GeForce 7900 GTX
I tested a heavy model with the following configurations:
*** Config 1 ***
Is the example osgWindows with the 2 windows options
Producer::RenderSurface1 Producer::RenderSurface2
| |
cam1 cam2
This gives 2 cameras each on his rendering thread, and the CPU load goes
up to 90% (it almost saturate the 2 CPUs)
*** Config 2 ***
Same osgWindows example, but on the single window option, which gives:
Producer::RenderSurface
/ | | \
cam1 cam2 cam3 cam4
The 4 cameras share the same RenderSurface, each of them owns a
rendering thread, but the whole CPU load goes at 50% (saturate only 1 CPU)
*** Config 3 ***
osgViewer --stereo HORIZONTAL_SPLIT
Producer::RenderSurface1
|
cam1
This creates a single camera with its rendering thread (as I can see
from the stats), and thus saturates only one CPU (50%).
Now my questions are:
1) The 50% bottleneck of Config2 is due to the fact that the 4 rendering
thread must be in sync with the shared RenderSurface, which is a single
thread and thus can run only on 1 cpu? Is this limit given by Windows OS?
2) If so, I guess that's the reason that Config 1 performs better,
having 2 renderSurfaces dispatched on the 2 cpus.
3) Why doesn't the HORIZONTAL_SPLIT option create 2 cameras (similarly
to osgWindows with the 1 window config)?
4) In case I use passive stereo (HMD or 2 projectors, typically setting
horizontal span on nVidia driver to use the output of the 2 heads), the
only way to achieve the performances of Config1 is to create a "fake"
fullscreen, with 2 windows without borders?
Or is there a cleaner way?
Sorry for the trivial questions, but I should better clarify my ideas on
that before thinking about multiple GPUs...
Thanks a lot
Ricky
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