POV-Ray : Newsgroups : povray.general : Tracking down slow renders : Re: Tracking down slow renders Server Time
22 May 2024 07:19:39 EDT (-0400)
  Re: Tracking down slow renders  
From: Chris R
Date: 8 May 2023 10:55:00
Message: <web.64590ce25485baa9159bf83b5cc1b6e@news.povray.org>
Alain Martel <kua### [at] videotronca> wrote:

> > "Chris R" <car### [at] comcastnet> wrote:
> >>
> >> What I'm afraid of is that some interaction
> >> between anti-aliasing, radiosity, and reflection is causing an infinite loop
> >> measuring against thresholds.
> >>
> >
> > That's a really hard-core set of features to throw at POV-ray all at once, ha.
> > Especially with isosurfaces added to the mix. I have similar scenes where I had
> > to eliminate anti-aliasing altogether, if I didn't want to exclusively tie up my
> > machine for days...and this on an 8 core/16 thread machine!
> >
> > My gut-feeling is that the slowdown for your last block is AA-related.
> >
> > One suggestion would be to reduce the size of your Render_Blocks. The default is
> > 32X32 pixels, I think. I run complex-feature scenes at 8X8, which does improve
> > the overall rendering speed on multi-core machines, and *helps* to keep that
> > final render block from taking so much time. As Thorsten F. pointed out in an
> > earlier post last year, each Render_Block uses an individual core (or thread-- I
> > get the two confused.) By reducing the block size, the processor seems to work
> > more efficiently, and doesn't have to spend all of its time on a single block
> > (with a single core) while the other cores are sitting idle. Or something like
> > that!
> >
> > I may have the technicalities wrong, but a smaller block size can sometimes
> > speed-up the render. It definitely works for media and isosurfaces (but I'm not
> > patient enough to throw in AA as well; most of my renders lately are just
> > relatively quick tests of one thing or another.)
> >
> Yes, using smaller render blocks can absolutely help with some slower
> renders. That is, renders that are not particularly fast and don't tend
> to have long I/O pipes in use.
>
> In multithread computing, the cores, virtual cores, used IS the thread
> count. Cores = physical aspect. Thread = logical aspect. POV-Ray use one
> thread per core/virtual core unless +WTn is used.

I realized later that I had already increased my AA thresholds for the latest
run, to no effect.  However, a combination of decreasing the max_trace_level
from 30 to 10, as well as decreasing the block size from 32 to 8 seems to have
markedly increased the over all speed, as well as eliminating the days-long
rendering of the few problem blocks.

I think my radiosity settings were already looser than you were suggesting, and
I have been using the 2-value counts as recommended by Thomas de Groot a while
back.  However, if I start to see issues on other scenes, I'll do some
experiments with the importance feature again.

-- Chris R.


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