Cycles slows down over time


I have a strange issue with Cycyles and have got no clue what the reason is.

I’m rendering a big scene (about 9500px x 6000px) with a decent amount of textures. Polygon count is not that bad. When I start the rendering, Cycles goes pretty fast and counts the samples in 10 or 20 step increments (branched path tracing). The longer the rendering goes, the slower Cycles gets. At about half of the image, the samples increase by one sample at a time. This happens in areas the are no any more complicated than the ones Cycles started at. Sometimes they are even empty.

Maybe somebody can give me an advice how to keep the render speed constant across the whole image.

Graphic card is a Geforce GTX 770.


Hi there - here’s a quick update.

It seems as if the issue had to do with Windows 10. I’ve put a fresh install of Windows 7 Pro on that PC and the rendering keeps up its pace all over the frame.


ah, windows 10. I actually thank it for having finished to convince me to switch to Linux.
Don’t forget to mark your thread as solved if you think it is.

So Win10 is not a nice player with Blender & Cycles? Damn, it was the only option on my comp purchase so I can’t retro-install, and my experiences with trying a Linux OS haven’t been the most reassuring. Can you recommend a reliable path to a Linux install, Caetano?

Linux Mint is a pretty good and user friendly all rounder. I used it for a couple of years, and used to be a part of their support team.

Now I’ve switched to Arch, having built LFS but found it too high maintenance. The likes of Arch and Gentoo are probably not great starting points for Linux newbies, though, since both require a good understanding of the underlying configurations across the whole system. Having said that, the Arch wiki is probably the most comprehensive one out there and can certainly be used for troubleshooting other distros when you hit a problem.

Yeah Windows 10 has some known issues with Blender, especially with GPUs.
I’ve also started on Linux Mint and I am still on it. It’s the most resemblant to Windows and one of the most used distro. Also I installed it in dual boot with Windows so that when I don’t know how to do something with linux and don’t have the time to find out, I can quickly boot on Windows and do it there. It takes a while to install it like this properly, you would need to understand partitions better than Windows has taught you.

Other than that I’m really a noob with Linux and so far it hasn’t been a problem. This distro is very easy to use.

Some of the links I used for the installation : : very useful tutorial this one I read entirely and it was very helpful for the dual boot installation and useful knowledge overall (this link is given in the first tutorial).

Thank you for the links, Caetano, looks like excellent information.


I can’t find where to mark the thread as SOLVED. Can you please give me a hint where to find it?


Edit first post - Go Advanced button. In “Prefix” select Solved and save changes