On Tue, 25 Jan 2000, Justin Cormack wrote:

> > 
> > Andreas Beck wrote:
> > > So IMHO one should rather _avoid_ multithreading, except for _large_
> > > independent tasks. The natural way to do this is in the user program, like
> > > separating input, scene calculation and rendering.
> This is certainly necessary.

Andreas is right. Look at how movie house developes a scene. They use
render farms. Toy Story used I believe 100 sun stations. Each station
rendered a seperate scene. Threads are useful when you access the video
hardware and have to wait for I/O completion.

> > Finally, this issue of having a multithreaded (potentially
> > parallelized) 3D pipeline in itself is, IMHO, very different
> > from having a THREADSAFE 3D pipeline.
> > If the 3D pipeline can be put in a separate thread (as a
> > whole), then it will probably be nice - because the application
> > can do its own work in another thread (and another processor).
> This is how glx now works, and means that dual processor boxes can
> work very well (although the load balancing is not very good for
> many programs, so much CPU time can be wasted).

Wrong. Utah-GLX is not threaded or SMP safe. XFree86 servers are not
threaded nor do they fork. I see a few post about how quake preforms the
smae on UMP and SMP boxes. Well its because Utah-GLX doesn't take
advantage of SMP. Remember GLX does everything in userland.

> It is adequate perhaps on a dual processor system. It doesnt work well
> above this. However paralllelising the pipeline has too many overheads
> due to accessing the same data. What is needed is parallel renderers,
> so that different threads can draw into the scene simultaneously.
> Also remember that hardware 3D is here to stay, and parallelising 
> the operations that will be done in hardware in the future is not
> very worthwhile.

You forget only one process should have access to a specific card. If you
parallelize the pipline such that the data is static thats shared then it
is a performance boost. Parallelising operations in hardware will be the
future. The next generation of voodoo cards will have 4 graphics
processors on them :)

Codito, ergo sum - "I code, therefore I am"
James Simmons                                                      (o_
fbdev/gfx developer                                      (o_  (o_ //\
http://www.linux-fbdev.org                              (/)_ (/)_ V_/_

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