[osg-users] Rendering performance issues

James Killian James_Killian at hotmail.com
Mon Jul 7 16:12:07 PDT 2008


I am so glad that someone else is getting the same results as we are.  I've
seen these same kind of gaps with our game and they come and go as I have
not been able to nail down the cause for them yet.  My guess is that there
is some external CPU I/O activity which is causing this, especially if the
graph representation works like a profiler class.  The last time I profiled
(I think around 8482) the threads looked very clean especially with minimal
critical section usage.

I guess the question for you, is can you profile your external CPU activity?
I use QueryPerformanceCount() and clock the time used for external code.  I
know for instance that collision detection has been expensive, and thus
causes the gaps.  Aside from this, if you have a Win32 platform you may use
SystemInternals tools like process monitor (formerly known as filemon) to
ensure your app is not doing some unexpected I/O operation.   I know for
instance that the trailed smoke particle effect will continuously reload the
image file everytime it is used... I wouldn't have found this if it wasn't
for filemon.  Perhaps there is some other implicit I/O surprise which is
happening to you.

I hope you can rule out the external workload, because perhaps there is some
performance change that we all can benefit from.  :)


----- Original Message ----- 
From: "Bob Balfour" <bob at BAL4.com>
To: "OpenSceneGraph Users" <osg-users at lists.openscenegraph.org>
Sent: Monday, July 07, 2008 5:37 PM
Subject: [osg-users] Rendering performance issues


> I'm experiencing some performance peculiarities that I don't quite
> understand. My platform is an HP Blackbird, Vista OS, 4-CPU, 2 NVidia
> 8800, OSG2.4.
>
> I have attached 4 timing images:
>
> 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?
>
> Now I flew thru the scene to a point where the Draw became quite small.
> The third image (vsyncON-app-short.jpg)  shows the Cull,Draw,GPU all
> <1.0, but I'm only achieving a 46Hz rendering rate because of the
> considerable gap between Draw and GPU.  Why is the GPU now being delayed
> so much after Draw?? It's almost like the GPU is stuck starting out
> there mid-frame?
>
> Now I turned VSync back OFF, but this time rendered TWO slave cameras
> (each 2880x900, one on each Nvidia card), and the same effect appeared
> (see the forth image vsyncOFF-2GPUs.jpg) where the GPUs are being
> delayed to mid-frame, and there is quite a delay after the GPUs complete
> (which should not be there with VSync OFF?).  Because of these
> substantial delays which I don't understand, performance has degraded
> considerably from my initial test image, which had good overlap and no
> delays.
>
> Is there any explanation for this, and can the delays be eliminated and
> performance improved?
>
> Also, is there a purpose/need for VSync using LCD flatpanel monitors or
> DLP projectors?
>
> Thanks.
>
> Bob.
> -- 
>
> Robert E. Balfour, Ph.D.
> Exec. V.P. & CTO,  BALFOUR Technologies LLC
> 960 So. Broadway, Suite 108, Hicksville NY 11801
> Phone: (516)513-0030  Fax: (516)513-0027  email: bob at BAL4.com
> /"Solutions in four dimensions" with *fourDscape*®/
>
>


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