[Radiance-general] multiprocessor systems, Radiance, and you

[Carsten Bauer]

Hi Schorsch,

ooops, for several weeks the Radiance-mailing list was more or less
'sleeping', but the issue of parallel processing still hasn't lost it's
fascination ... so I think no one would mind if I answer your question
right here:

I had the idea of making the processes as independent as possible, so in
the PVM version there's one master distributing the blocks, the workers
which do the tracing, a collector receiving finished scanlines (and in
the end  puzzles everything together for the big picture) and of course
the ambient slave, who receives amb. values and broadcasts them to all
the other workers. This ambient slave alone has access to the file for
storing them. Only at the beginning of a new run the workers can access
an already existing ambfile for reading in values.

It's important not to start in one corner of the image and distribute
the blocks regularly. The master picks them randomly from the list, thus
the process resembles a bit the rview style, which is more appropriate
for filling up the ambfile with values from the whole room, as Charles
pointed out. so sharing will happen mainly at the end of the run, when
more and more blocks happen to be adjacent to one already processed. 

Let's stop here, I don't want to flush the general list too much...

Except of course with general remarks :-)

This sort of parallel processing of one picture is only adequate for
really big images of really complicated scenes (btw, - this means
automatically that bottleneck problems are unlikely to occur). For usual
scenes and the majority of applications like sequences under different
conditions, lots of rtrace runs etc etc, distributing the job with
scripts or manually on some machines is easier and more efficient.

A different thing is of course the idea of using PVM to couple OS X or
Windows and Linux machines, which might be interesting for bureaus who
already have lots of hardware standing around. And another different
thing is thinking about the future, what about parallel processing for
the photon-map ? I know that some have objections against using external
libraries, but at the same time its inefficient to reinvent the wheel
again and again, so why not use the features PVM has to offer?

-Carsten