CPU Xparts & Yparts Relationship

Hi All,
I was just rendering a scene an noticed that Blender was only using 25% of my CPU even when I had 4 CPUs selected. It took me a little while but I figured out that the Xparts & Yparts are related to CPU usage as well. I had set my Xparts & Yparts to 1 to get a “crisper” look out of my render. But it seems that when you do that, only a single CPU gets used.

I guess parts are portioned out to CPUs at render time.

Not really a question here, but just an observation.

What do you mean “crisper” look? :S Shouldnt it make the image look same even if you have only 1x1 or 4x4 parts… :S

I’m not sure if/why it looks different, but I know each render is split up into rectangles. By default, there are 16. Only one core (thread) is allowed to work on a rectangle at a time, and that core may not work on more than one rectangle a one time.

So if you have a quad-core processor, and you have 1 rectangle, only one of those 4 is going to be used. Divide up the image into 4 (2,2) and then see how much faster it is.

I thought that Xparts and Yparts feature is useful for lowering CPU usage of render. But it sounds logical that if you have 4-core, there should be total number of “patches” some multiple of 4. So every core is rendering different patch and should be involved in rendering to the end.

But you know. some patches are rendering faster (for example simple gradient), so in the end not all cores will render same amount of patches.