[Radiance-general] rtrace -n question

[Andrew McNeil]

Hi Rob,

When there is no ambient file there is usually an ambient cache created in
memory.  If you don't have an ambient file each rtrace process will build
its own cache.  I'm guessing that each process spends most of the time
building the cache with a first point and the subsequent calculations are
very quick.  Because getting the cache to saturation is the majority of the
calculation time and each processor is doing this independently before
really getting going on the points it won't matter if you have 1 or 16
processors, the simulation will take the same amount of time.

To completely turn off the ambient cache use -aa 0.  I expect you will see a
linear correlation between number of processes and simulation times, but the
sim times will be much much longer.

On a side note, I'm very jealous of your 16 core mac pro!

Andy




On 12/17/09 8:30 PM, "Rob Guglielmetti" <rpg at rumblestrip.org> wrote:

> Hi everyone,
> 
> So ah, I played with the rtrace -n option a bit, and got results I don't
> understand. Anyone interested in having a look, please visit this page:
> 
> http://www.rumblestrip.org/interests/light/rtrace-multiprocessing-option-initi
> al-test-results/
> 
> - Rob
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> Radiance-general mailing list
> Radiance-general at radiance-online.org
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