Big rendering slow down at 99% (mental ray)

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Maximus
Posts: 1104
Joined: 09 Jun 2009, 15:45

Big rendering slow down at 99% (mental ray)

Post by Maximus » 17 Sep 2011, 13:33

Hey guys, i've experiencing this problem quite a bit and was wondering if anyone had this issue.

Basically the rendering stops using all cpus at 99% of the rendering process, and to accomplish 100% it takes a bit of time, probably more than it should.
I've noticed that this happens when there are heavy things to calculate, in my recent scene i was using a high sampling values on glossy, like 254 samples, and the output image was 2K.

It happened other times too with displacement, and other heavy calculation, sometimes it happen when i'm using lots of instancies, strands for grass with scattering, well you got the point, when there is a lot of heavy stuff to calculate.

Happened to someone else? Its kinda noticeable especially when you have big output images you'll see the render stuck at 99% for a bit, then it completes.

I'm not even sure if it is an issue because to compute the last bucket anyway it requires time, but what is weird is the total drop of all 12 cores to almost 0, for the 1% remaining rendering task.

Thanks, Max

luceric
Posts: 1251
Joined: 22 Jun 2009, 00:08

Re: Big rendering slow down at 99% (mental ray)

Post by luceric » 17 Sep 2011, 23:24

probably a consequence of mental ray now having the frame buffers on disk, so at the end maybe it needs to reload the tiles from temp files, assemble the final image and write it the whole thing back.

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Maximus
Posts: 1104
Joined: 09 Jun 2009, 15:45

Re: Big rendering slow down at 99% (mental ray)

Post by Maximus » 18 Sep 2011, 13:04

thanks luceric for the explanation, guess nothing can be done?

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