POV-Ray : Newsgroups : povray.general : Threads and rendering performance : Threads and rendering performance Server Time
23 Apr 2024 13:34:06 EDT (-0400)
  Threads and rendering performance  
From: Chris R
Date: 30 Nov 2023 09:25:00
Message: <web.65689af546bcd7a113355b545cc1b6e@news.povray.org>
I recently got a new laptop where I do my renders and noticed an issue where it
would just completely freeze up, to the point where I had to do a hard
power-down to get it to respond while rendering with POV-Ray.  It appeared to
only happen if I was doing a large render, (multi-day even), and tried to do
something else on the machine while it was running.

So, I looked into limiting the number of worker threads in POV-Ray to make sure
there was always some spare capacity to do other things without triggering
whatever Windows 11 bug is causing this.  My machine has 14 cores and 20 logical
processors.  Running with the default settings, it would peg all 20 logical
processors at or near 100% when doing a large render.  Doing some experiments I
verified that worker threads take up one logical processor (vs cores).  I ended
up settling on a new default using 12 worker threads instead of the max, which
based on performance monitoring tools runs at about 50% overall CPU utilization.

The odd thing I've noticed, though, is that my renders are not significantly
slower.  In fact, the holiday scene I posted recently took almost 4-days to
render at full bore, but in a re-render with some settings that should be
slowing it down, its about 71% complete after 16 hours, using only 12 workers.
(Note: this is anecdotal evidence; it's possible the last 29% of the pixels are
significantly slower to render due to more glass reflections, etc.).

So, now I'm wondering if there could be some thread interactions that are
getting overwhelmed when using all of the cores, or if using all of the cores
causes too much heat, so the machine is slowing things down internally to
compensate, or something else?

I just thought it was interesting and maybe someone else has experienced this
before who might have some insight into it.

-- Chris R.

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