Robert,
I believe this to be a driver issue as well. However, what it does show
is that it is probably preferable to have different contexts on
different cores, also to eliminate any possible opengl driver overhead.
On 2 cores it runs perfectly as expected; same frame rates as
stand-alone. On a single core they both drop back a little, probably
because the quadro opengl driver is eating up a lot of CPU time for some
obscure reason. Even when the opengl implementation is set to
multi-threaded, I never see it start using any additional core by
itself. This only happens when you set the affinity manually. So fully
relying on the OS scheduling may not be the best option.
I don't remember the exact stats, and I can't check them now as I don't
have the machine here. I think it was something like 0/0/x for the 8800
and 0/y/y for the 5600, with x close to y.
Robert Osfield wrote:
Hi Ferdi,
It sounds like the OpenGL driver is not behaviour well in your case
and twisting the results from what you would normally expect. With
scene of 25M polygons you are almost certainly GPU/bandwidth limited,
and pretty likely that the OpenGL fifo is backing up and playing
havoc. Multi-processing is this situation is not really going to make
a huge difference in terms of potential gain because the bottleneck is
elsewhere - you aren't CPU limited, it shouldn't make things worse,
and the fact that it is suggests that the driver is having issues.
What are you cull/draw/gpu stats?
Robert.
On Thu, Dec 4, 2008 at 10:43 AM, Ferdi Smit <[EMAIL PROTECTED]> wrote:
I've been looking into thread/process affinity with respect to a dual-GPU
setup. This is what I found back then:
2 processes, CPU affinity on different cores, each renders the full scene on
a different GPU
OSG_THREADING=SingleThreaded
(1 core shows heavy use, 2nd core show moderate use, 2 cores idle)
Quadro 5600 8800GTX
Multi-GPU / Multi-Processing 16 15 (fps)
OSG_THREADING=ThreadPerContext
(CPU Affinity is set but appears to be ignored: 1 core shows heavy use,
others idle)
Multi-GPU / Multi-Processing 11 14 (fps)
So, yes, it helps if the CPU load is balanced across cores, even for this
simple 25M polygon scene that is for 99% GPU. Also, OSG seems to mess up
manual settings when set to multi-threading :) Check CPU loads in the
performance monitor. Don't let 3 cores stand idle all the time; it's a waste
of available processing time, and this will only get worse in the future
with more cores.
Side note, I finally received my 4GB memory, so I can get this quad core,
dual GTX260, pcie 2.0 machine running :) Let's see if it behaves differently
from a Quadro+8800 on pcie 1.1.
Ulrich Hertlein wrote:
Additionally: what is the communities' experience with manually assigning
processes to cores? Does it work?
It sounds like a good idea but in my experience it's best to leave the
scheduling up to the operating system to handle core affinity (except when
you're running Windows which has a completely fscked-up round-robin
scheduler).
Cheers,
/ulrich
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Regards,
Ferdi Smit
INS3 Visualization and 3D Interfaces
CWI Amsterdam, The Netherlands
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osg-users mailing list
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Regards,
Ferdi Smit
INS3 Visualization and 3D Interfaces
CWI Amsterdam, The Netherlands
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