[Radiance-general] genBSDF multiple processes

[Stephen Wasilewski]

Thanks Greg,

That makes sense, although it seems there might be something else going on
as well.

my model is purely specular and has no transmission only reflection.  I ran
through a number of -c options last night with '-t4 6':

-c 10240 (2.5 samples) took ~ 20 minutes
-c 40960 (10 samples) took ~ 1.5 hrs
-c 102400 (25 samples) took ~ 3.75 hrs

so it seems calculation time is scaling linear with my count.

I have a large number of polygons (the rad file is 31 MB) and my material
is a mirror with a brightfunc modifier (the glass_angular_effect you shared
a number of years ago.  does that introduce some other bottleneck?

Stephen Wasilewski
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On Tue, Oct 4, 2016 at 7:07 PM, Greg Ward <gregoryjward at gmail.com> wrote:

> Hi Stephen,
>
> The rcontrib command underpinning rfluxmtx and therefore genBSDF can
> become i/o bound if the model is not particularly complicated and/or there
> are few non-specular rays being generated.  If your system is purely
> specular, this is the sort of behavior I might expect.  As the number of
> receiving bins increases from -t4 5 to -t4 6, you go from 1024 output
> directions per input direction to 4096.  If you leave your sampling (-c)
> parameter at 2000, then you're actually sending fewer samples per incident
> direction than you have output bins.  This might be OK, depending on your
> model, but it means that the number of bin results being sent from one
> process to another exceeds the number of rays being calculated, thus i/o
> becomes the bottleneck over CPU if you have enough processes.  In a sense,
> you could increase your -c setting by a factor of 2 or 3 and get better
> accuracy in the same calculation time.  Try it and see if it doesn't
> improve your CPU utilization.
>
> Remember that if your number of processes exceeds the number of physical
> cores (not virtual ones), then your time-linearity will go down
> dramatically, even if your CPU utilization shows 100%.
>
> Cheers,
> -Greg
>
> *From: *Stephen Wasilewski <stephen at coolshadow.com>
>
> *Date: *October 4, 2016 6:14:24 PM PDT
>
>
> I'm getting some curious (to me) behavior when running genBSDF to
> calculate a rank 4 tensor tree (It also happens with '-t3').  When the
> sampling resolution is 4 or 5 the program utilizes most of my processing (I
> notice it starts 9 rcontrrib processes an 1 rfluxmtx process with '-n 8',
> so the threads are each around 80%).  When I change the resolution to 6
> (without changing anything else) the processors top out at 25% and if I
> increase -n it still uses no more than ~25% of my total cpu power.  There
> is plenty of unused memory.
>
> here is my command:
> genBSDF -n 8 -c 10240 -f +b -r '-ab 10 -ad 1 -ss 0 -st .02' -t4 5 -dim 0
> 2.673 0 2.706 -1.207 0 -geom millimeter test.rad > test.xml
>
> Does anyone know what is going on?
> Is there something in the genBSDF program limiting this?
> Is it a hardware limitation?
> Is it some environmental variable (im running mac OSX 10.9.5)?
>
> Thanks,
>
> Stephen Wasilewski
> *LOISOS *+* UBBELOHDE*
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>
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