I have noticed this happening in any render I do, no matter which file or contents. If something takes me 15 seconds to render with the render window in the foreground, the same render might take 30-40 seconds if the render window is in the background. I cannot find a single post on Google about this. I’m not sure if this is a Windows thing or a Blender thing. I do know that many years ago when I used to use 2.78 on Win7 this did not happen.
I have tried setting task manager priority to high, realtime, etc, and in Nvidia settings I’ve tried turning on ‘prefer maximum performance’ and ensured the ‘background app max frame rate’ is off – none of this improves anything. And when Blender is rendering in the background I am not doing anything intensive. Maybe just reading the news. I have tried just putting Blender in the background and not touching anything – but it still increases the render time.
Hmm this would be odd indeed. Usually programs need longer if showing anything to the user because of the additional drawing on screen. If nothing is shown the image is only once drawn on screen when the user puts the app in the foreground (or it is popped up).
(quick test on linux: multiple render with and without switching to another fullscreen window… no difference noticable)
Long shot here and while I understand you are GPU rendering, Blender is still running and the CPU would be still ‘directing’ the rendering, even tho the GPU is doing all the hard work.
The reason I’m talking about the CPU is I notice you have a new Intel 12th Gen, which has P and E cores. However, you are running Win 10, which unlike Win 11 doesn’t really know how to handle/deal with the CPU’s ‘split core’ design.
I think you can test this easily, in that in the BIOS, it should be possible to disable all the E cores, making the CPU look and work just the same as every CPU before it, which Win 10 knows exactly how to handle.
Good idea thanks, but unfortunately it did not have any effect.
Though I’ve just realized what is making it take longer. Denoise, specifically OpenImageDenoise. If I change to Optix denoiser, or disable completely, it renders just as quickly while minimized. But Optix does not look as good. So hmm I am wondering if this is just a bug or something fixable.