POV-Ray : Newsgroups : povray.general : Tracking down slow renders : Re: Tracking down slow renders Server Time
10 Dec 2023 12:27:00 EST (-0500)
  Re: Tracking down slow renders  
From: Alain Martel
Date: 8 May 2023 10:31:18
Message: <645907b6$1@news.povray.org>
Le 2023-05-08 à 10:04, Chris R a écrit :
> "Kenneth" <kdw### [at] gmailcom> 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.)
> Thanks for the suggestion.  I had done that in the past, but forgot about it.  I
> should just make it my default instead since it would probably help most of my
> renders anyway.
> I'm going to try some of the other suggestions as well.  The latest render
> completed 99% in about 2 hours, and then just sat there for 2 days on the last 2
> blocks.  I'm afraid without any other adjustments, I'll get to 99.9% using
> smaller blocks, but that last 0.1% will then take two days.
> -- Chris R.
Using smaller blocks I got a render that would get stuck on the last 
render block for days to finish in only a few hours.

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