[Radiance-general] rtrace -n question

[Greg Ward]

I agree with Andy's assessment.  I also don't think you'll see a  
linear acceleration past 8 processes, as the MacPro doesn't really  
have 16 processors, only 16 threads on 8 cores.  It's not nearly the  
same, which is why I'm holding out for more processors before I  
upgrade my old PowerMac G5 Quad.

-Greg

> From: Andrew McNeil <andrew.mcneil at arup.com>
> Date: December 17, 2009 11:00:00 PM PST
>
> 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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