[Radiance-general] rtrace -n question

[Rob Guglielmetti]

OK, thanks guys. It's not as if I wouldn't use caching normally, I just saw something that didn't make sense to me. Thanks for straightening me out. 

As far as the hyperthreading, I did do some tests and it seemed to be nearly linear to 15 or so, for mkillum at least. But those weren't as controlled as the testing I did yesterday with rtrace -n. I'll have to look at that some more. Anyway thanks guys!

- Rob

On Dec 18, 2009, at 8:47 AM, Greg Ward wrote:

> 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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