Hi Dominik,
On Mon, 2006-02-13 at 11:07 +0100, Dominik Rau wrote:
> Hi.
>
> I'm a little bit despaired in configuring my setup, maybe someone of you
> can give me some hints.
>
> Under my desk, there's a bloody fast XW9300 Dual-Opteron (single core,
> 2.4GHz) HP-Workstation with 2 Quadro 3450 Cards, connected to 2
> 1280x1024 Displays and 2 1024x768 video projectors. As the OpenGL Window
> Size is limited to 4096 (I don't know whether this is Nvidia or OpenGL
> specific), I have to use the multi display window on the localhost.
It is OpenGL, but I'm not sure why that's a problem. You could put them
on top of each other to get down to 2560x1790 or 3304x2048 or so. But
you have two cards which have to be run by a separate X server, which is
the main problem.
> Unfortunately, it does not work the way I want. Problems start already
> if I use only one window on two of the four displays: If I display my
> scene with a SingleWindow using the GLUTWindow/SimpleSceneManager, the
> scene runs perfectly smooth. If I use the same scene with the cluster
> window, connected via StreamSock to 127.0.0.1 there are a lot of short
> hangs that are not acceptable. If i print the FPS, I get exactly 75FPS
> (SyncToVBlank, Display running at 75Hz) with the GLUTWindow, and
> everything between 45 and 65 running the cluster window (which is quite
> strange, as it should be synced too.)
Networking is always somewhat unreliable for real-time apps, as there
are always buffering effects and process switches.
> Ok, maybe I should mention, that I play 2 (and more) videos in my scene
> and that there's a throughput of >70MB on the loopback device, but this
> shouldn't be a big problem for this machine, there's also plenty of
> headroom on both processors.
You'll probably run into OS buffering and waiting. The problem with
real-time apps is that a couple ms lost mean dropped frames. Running a
single process even the Linux kernel is good enough to be faster than
that. But if multiple processes are running this becomes pretty hard. On
the old SGI boxes you could isolate and dedicate processors to specific
processes, not sure if Linux allows that.
> So, what's my problem? Any ideas? Has anybody a similar setup?
>
> Nevertheless, even if I can get it to work on the loopback device, I
> fear that if I want to use a similar scene in a real cluster, even my
> GB-Ethernet can't handle this.
Is that the target configuration? If it is, we don't have to worry about
single machine problem.
> Is there a way to reduce the amount of
> data sent over the network?
Fewer changes. ;)
> Is it possible to compress the changelist?
The changelist itself is not big, the data sent over is the problem,
especially if you run videos.
> Or to use local copies of a video?
You could, by changing the servers to decompress the video locally into
the used texture. You would need to identify it, and synchronisation
will be interesting.
> I had similar problems with Rasmus'
> Animation Library, where a lot of vertices were transformed per frame
> and every changed vertex was sent over the network instead of the
> corresponding fraction value in the time sensor. How can I solve this?
The OpenSG clustering approach is based on the idea that all changes to
the scenegraph should be automatically shared to make it easy for apps.
If you change a lot of data (i.e. morphed vertices or video frames) that
can become a problem. The best way to fix this is to move these
expensive operations inside the scenegraph, e.g. transmit the time
change and do the actual morphing in the rendering traversal (or an
update traversal, once we have one). Same thing for the video, the best
way would I can think of right now would be to create a
VideoTextureChunk or something similar that decodes the video to the
desired frame/time when it's activated. That way only the time change
needs to be transmitted.
Hope it helps
Dirk
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