Cycles CPU vs. GPU performance

CPU baking:
CPU usage at 100%, slower baking, but system remains responsive and usable for other tasks.

GPU baking:
CPU usage drops to 15-20%, faster baking… but system is extremely sluggish and basically unusable for other tasks.

This seems a little counterintuitive, although I’m sure there’s a perfectly logical explanation that involves shuttling data back and forth between the CPU and GPU and whatnot.

However: is there any way of improving system responsiveness when using Cycles GPU baking?

FYI, the computer is a quad-core i7 (8 virtual cores) running Win 7/64, 12 GB RAM, and an nVIDIA GeForce GTX 660 Ti (2 GB)


The reason why your computer feels sluggish is that the graphics card is only updating the screen a few times a second, rather then 60 times per second (most monitors operate at 60fps)

The reason for this, is because your graphics card is being stressed to the max doing other computations other then displaying graphics.

The fix, is to get another graphics card for display purposes only.

Thanks for the reply :slight_smile: I see what you’re saying… but although I can’t quite put my finger on it, it feels as if it’s not just a refresh issue. Are there any other possibilities?

Ok, so I went and bought myself a new motherboard, a new CPU, and new graphics card (GTX 780 Ti). I kept the old graphics card installed (a GTX 660 Ti) as well, so now the two cards are driving separate monitors.

The 780 is over twice as fast as the 660, which is awesome. Fun fact though: enabling both cards in User Prefs is actually slower than using only the 780…

The reason why both are slower then just using one is because they are of significantly different speeds… which means that the 780 will finish tiles quicker than the 660… which means that the final tile will probably be done by the 660.

Best bet is to try to increase the number of tiles, try going for a standard size for tile sizes (so if your render size is 1280… try going for 640 or 360, instead of 400 which doesnt neatly go into 1280), try different tests between 8-24 to see whether you can improve on the speed or not.

What you can do, is have no monitors hooked up to the 780 if you want to leave it dedicated to rendering, this works fine under windows.

didnt see this response sorry… if ever i dont reply and you want an answer just pm me.

Pretty much what happens when rendering is that it takes up 100% of the gpu ALL THE TIME…its not like in games where it processes the frame and gets a slight rest before processing the next frame… rendering takes minutes / hours to finish… so the gpu doesnt get a rest to update the UI.

Thanks again for replying :slight_smile:

I’m actually baking, not rendering… do tile sizes matter in that context? I did some quick tests earlier and it didn’t seem to baking affect performance.

I’m going to tinker with the setup for a bit and see what works best – basically unpacked everything a couple of hours ago (oh, the new gadget smell… :slight_smile: )