I use progressive mode all the time with a GPU but some people have pointed out this is a slow method to render, below is a suggestion why

I'm assumimg here that the GPU should run at 100% all the time to get the best render times.

Metrics from the tests run on a 6700K + GTX1070 - underclocked to get 800MHz. Graphs from MSI-Afterburner

Using "Render to Background" appears to run the best with minimal drop (not tested but "Render to Queue" should also work well)
Standard Render (non progressive) has a small performance hit which increases with slower CPUs.
Progressive mode has a significant performance penalty particularly when rendering large images

CPU speed - GPU Utilisations 4.3GHz vs 0.8GHz

Progressive Mode and image size. This effect is not significant with the other two render methods

What are the render times for each of the test?

Progressive render is slow, its slow like Poser or in Blender, I tested several times that like with CPU only or with GPUs

You can check GPU usage in SIV64 or HWiNFO to see in more detail what GPU usage it is, during the progressive rendering although MSI Afterburner outputting 99% usage but in reality is something like 70-80% usage

With tile rendering its similar GPUs usage in my case is like 70-80% as max, seen only on few occasions higher GPU usage in 85%

Hope this helps

Thanks, Jura

Friends don't let friends render in progressive mode.

@3D-Mobster - I didn't time the renders as the "Render to Background" doesn't display its time making comparison difficult. Progressive mode appeared to add around 10%-20% so for quick renders not much of an overhead but for one taking several hours it becomes more significant

@jura - thanks for the info, will check those two programs.

@ghostship - I can see why now although I think its still useful for initial lighting tests if not the full render.

Looking at the 4.3GHz vs 800MHz comparison, the 800MHz "Render to Background" run had a blip when the screen updated but otherwise looks fine - this has got me thinking maybe an old PC + new GPU when used as a render node will work just as well as a new PC. Curious if anyone is doing this. Also curious if anyone is using queue manager+gpu+linux combination.