Hello Jason, On Jan 27, 2012, at 1:37 PM, Jason Daly wrote:
> On 01/27/2012 02:12 PM, Paul Martz wrote: >> Sorry, I was going off your post that read "This leads me to believe that bus >> contention was causing the lack of scalability." I was just trying to >> outline a >> way to validate that suspicion. If you've already ruled out bus contention, >> then >> disregard my post. > > Hi, Paul, > > I'm not dismissing your post at all. It's certainly worth thinking about the > overall bandwidth, and how much of it might be consumed by the GL command > stream. I like your equation as a general guideline. One just has to keep > in mind that 500MB/sec is the bandwidth for a single PCI-e 2.0 lane. Most > graphics cards get 8 lanes, if not 16, and that's per card. You also have to > account for the CPU interconnect bandwidth, which may put an upper limit on > how much data you can transfer with multiple cards (theoretically 12.8GB/s on > this hardware). > > In this particular case, I think Tim is right. There's not enough data in > the command stream to get near the bus bandwidth. In this case, there are > two 8x PCI-e cards (total of 8GB/s bandwidth) feeding 4 GPU's (two QuadroPlex > D2 units). Using your figures: > > 2 * 8 * 500 MB/s > ----------------------------- = 5648 Hz > 4 * ( (5500 * 64 B) + 2048 B) > > > So, unless I'm missing something, the problem must be elsewhere :-) We run a very similar system with 5 quadro cards and do not run into these problems with very large models. We are using VR Juggler though. I mention this because it would be very straight forward to use one of the sample OGL VR Juggler examples as a test application that would load an OBJ file or something to provide a raw OGL benchmark for the hardware. You could also use one of the sample OSG applications to do a comparison to at least provide a place to start working from in terms of figuring out your core issues. Doug _______________________________________________ osg-users mailing list osg-users@lists.openscenegraph.org http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
