POV-Ray : Newsgroups : povray.windows : Massively delayed Stop Render : Re: Massively delayed Stop Render Server Time
27 Sep 2021 06:28:35 EDT (-0400)
  Re: Massively delayed Stop Render  
From: clipka
Date: 19 Mar 2016 21:31:04
Message: <56edfd58$1@news.povray.org>
Am 19.03.2016 um 23:49 schrieb Bald Eagle:
> So, I've noticed that sometimes when I'm rendering a very large sized graphic
> (10240 x 7680), that things slow way down, memory usages goes way up, and
> clicking on _stop render_ is apparently unresponsive.
> Then I wait while POV-Ray happily renders away - and then registers my stop
> render - like minutes later.
> 
> I this a POV-Ray thing, a Windows 7 thing, a Dell Inspiron thing... ?
> Has anyone else noticed this behaviour?
> 
> Win 7 Home Premium SP1
> Dell N5110 i5-2410M 2.3 GHz
> 4GB, 64 bit
> 
> Running 3.7.0.msvc10.win64

This is a known effect for large images of simple scenes: For
sufficiently large images, the buffer in which POV-Ray assembles the
rendered image chunks into a complete image is not held in main memory,
but in a temporary file instead. As a consequence, the performance of
the thread that does this assembly is limited by the disk I/O bandwidth.
On the other hand, the render tasks that compute those chunks are
limited only by processing power and main memory bandwidth, and so in
simple scenes they may crank out results faster than the image assembly
thread can consume them. In such cases, the rendered chunks pile up in a
queue held in main memory, which grows larger and larger as render
progresses.

Of course it doesn't help that as the queue grows larger, chunks spend
more and more time in the queue, and are thus more and more prone to be
swapped out to disk by Windows' virtual memory management, creating even
more disk I/O workload.

As for the delay when stopping the render, it is important to note that
the queue of rendered chunks is actually a generic message queue, and so
the image assembly thread first has to process all the piled-up chunks
before it even receives the information that the render is to be
stopped. (Or at least that's what I think is happening; I'm currently
not deep enough into the details to say for certain. An alternative
explanation might be that the delay is caused by POV-Ray struggling to
release all the memory blocks holding the image chunks.)


> Also, every so often F1 (Help) doesn't respond either.

To my knowledge, this is entirely unrelated.


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