On Mon, Dec 13, 2010 at 9:51 PM, Steve Satterfield <[email protected]> wrote:
> > Hi, > > I would like to update the discussion we started back in October > regarding an apparent problem scaling OSG to multiple windows on > multiple graphics cards. For full details on the previous discussion > search the email archive for "problem scaling to multiple cards". > > Summary of the problem: > > We have a multi-threaded OSG application using version 2.8.3. (We also > ran the same tests using version 2.9.9 and got the same results.) We > have a system with four Nvidia FX5800 cards (an immersive cave like > config) and 8 cores with 32 GB memory. > > Are you using Linux? > Since the application is parallel drawing to independent cards using > different cores, we expect the frame rate to be independent of the > number > of cards in use. However, frame rate is actually X/N where N is the > number of cards being used. > > For example if the frame rate is 100 using one card, the frame rate > drops to 50 for 2 cards and 25 for 4 cards in use. If the > application worked properly, the FPS would be 100 in all cases. > > > We have tried a number of things to isolate the problem: > > ... > * We have created a pure OpenGL threaded application which draws to > 1, 2, 3, or 4 cards. There is no OSG involved. This application > runs properly, no degradation in FPS for multiple cards. > > Could you share the source of this program? > * When we set OSG_SERIALIZE_DRAW_DISPATCH to OFF (default is ON) > the total FPS actually drops. Watching the graphical statistics, > the DRAW is clearly running in parallel, but is actually a bit > slower than when the DRAW is serialized. > > While this behavior is consistent with the messages posted by > Robert in August 2007 (search for OSG_SERIALIZE_DRAW_DISPATCH), > its not what one would think should happen. Specifically, it > seems counter-intuitive that serialized DRAW is faster than > parallel DRAW. > > It is paradoxical. That it works at all is do to the fact that, with vsync enabled, all GPU activity is buffered up until the after the next SwapBuffers call. ... > OSG is a critical component to our immersive virtual reality > environment. Our scientific visualization applications are continuing > to demand more and more performance. We need multi-threading to work > properly. > > What experiences are others with multiple cards having regarding > multi-threading? If anyone is interested, we can send our test program. > > We would very much appreciate any help or suggestions on solving this > problem anyone can offer. > I put together a multicard system specifically to look at these issues, and I too am very interested in getting it to work. Tim
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