[Radiance-general] why the rtrace "-n" option doesn't reduce simulation time ?

[Ji Zhang]

Thank you very much, Greg!

Following your advice, the simulation time is reduced from 9 min to just 3
min !

The bash script is:
cat ./sensor.txt | rtrace -I -h -w -oov -u- -aa 0.1 -ab 6 -ad 1024 -ar 256
-as 512 -af ./ambient_file.amb -n 8 ./Octree_files_.oct > ./Results.txt
(I'm very eager to test it on our HPC later ! )

I think this can be one of the FAQs of Radiance.

Thank you again! And have a nice weekend!

-Ji


On Friday, October 19, 2012, Greg Ward wrote:

> Hi Ji,
>
> This has been discussed before in an earlier thread -- some months ago, I
> guess.  You don't get a speed-up from parallel processing if you fail to
> set the -af option to share indirect values.  This is because you force
> each process to recompute the same values redundantly.  Add a -af option
> and see what happens.
>
> Cheers,
> -Greg
>
> > From: Ji Zhang <hope.zh at gmail.com <javascript:;>>
> > Date: October 19, 2012 8:02:47 AM PDT
> >
> > I did the same Radiance simulation, one without specifying the "-n"
> option for rtrace, the other with "-n 8" specified for rtrace. The former
> took 9 min to finish, whereas the latter used 13 min ...
> >
> >
> >
> > I was quite happy to see all the 8 cores of the CPU are fully utilized
> in the beginning, but I was quite upset when the results turned out to be
> worse than not specifying anything ...
> >
> >
> >
> > Why the -n option didn't reduce the simulation time but increases it ?
> ...
> >
> >
> >
> > Did I miss something obvious here regarding Radiance parallel rendering ?
> >
> >
> > The two bash scripts are something like:
> >
> > oconv ./Sky_m3_d21_h13.rad ./materials.mat ./Context.rad >
> ./Octree_files_m3_d21_h13.oct
> >
> > cat ./sensor.txt | rtrace -I -h -w -oov -u- -aa 0.1 -ab 6 -ad 1024 -ar
> 256 -as 512 ./Octree_files_.oct > ./Results_m3_d21_h13_ir_RGB.txt
> >
> >
> >
> > and:
> >
> >
> >
> > oconv ./Sky_m3_d21_h13.rad ./materials.mat ./Context.rad >
> ./Octree_files_m3_d21_h13.oct
> >
> > cat ./sensor.txt | rtrace -I -h -w -oov -u- -aa 0.1 -ab 6 -ad 1024 -ar
> 256 -as 512 -n 8 ./Octree_files_.oct > ./Results_m3_d21_h13_ir_RGB.txt
> >
> >
> >
> > The test was done on a Macbook Pro, OS X 10.8.2, 2.3 GHz Intel Core i7
> (8 cores), with 8GB REM.
> >
> >
> >
> > The images showing the CPU core usage for the two simulations are put at:
> >
> >
> http://episode-hopezh.blogspot.sg/2012/10/rtrace-parallel-rendering-myth.html
> >
> >
> >
> > Advices are appreciated! and thanks in advance!
> > - Ji
>
> _______________________________________________
> Radiance-general mailing list
> Radiance-general at radiance-online.org <javascript:;>
> http://www.radiance-online.org/mailman/listinfo/radiance-general
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.radiance-online.org/pipermail/radiance-general/attachments/20121019/fb27fac6/attachment-0001.html>