I think this subject often come back on this forum (for example here )
Please don’t forget to make a search before creating new topic
To come back to your problem : when you check
CPU+GPU , computation power will be shared per tile on the render. For example :
- Let’s say you have 2 x RTX 2080 Ti , and a 8 cores CPU . If you render on 8 tiles. 2 will be given to GPUs, and 6 will be given to CPU. The GPU finish very quickly, and then your’re waiting for CPU to finish there tiles, during like… an eternity. Whereas if you uncheck CPU, the GPUs are doing both 8 tiles and it’s MUCH MUCH faster.
BUT If you have 200 tiles to render, and a very fast CPU, using the CPU in addition to the GPU can be better, because when GPU is doing some tiles, CPU will “save” time by computing some others
To sum it up, in fact it’s not a matter of tile size (32x32, 64x64, or wathever) but only a matter of optimisation considering number of tiles to render. If both GPU and CPU will work during ALL the render, it’s the best configuration. As soon as a tile configuration leads to a GPU stopping it’s work, and letting CPU’s do all the remaining tiles, it’s bad.
See you ++