I have two computers running side-by-side both rendering frames from the same animation, but one machine is rendering much slower than the other despite being only a slightly lower CPU speed. How do you pin-point the cause of such a thing?

My main PC is a Core i7 3.3 Ghz 6-core and renders the frames in this animation between 3 and 5 minutes. The secondary is a Core i7 3 Ghz 4-core and renders from 15-35 minutes. Now, best-case, I would expect the slower PC to take less than twice as long to render the same frame. At first, I was network rendering and I thought the difference might be due to something there. So first, I made a copy of all the maps on the secondary’s local drive. No difference, so I ended up just copying the whole scene and all assets over to the secondary and then rendered the scene locally. Still have the much slower rendering. . .

I’m not getting any error messages and the renders are fine visually. I’m also not seeing any obvious performance issues outside of the slow rendering. I don’t know how to go about figuring out the bottleneck in this case. Anyone have any tips for tracing something like this? Much appreciated!

Brian

The machines are very similar in configuration, only the CPU and RAM amount are different. Same OS and software loadouts otherwise. The slower PC still has 12 GB of RAM though and the scene isn’t using anywhere near all the RAM, so I don’t think that is slowing it down.

I did the math on the speed difference and rounded up, which is why I was saying I expected the slower computer to take no more than twice as long. Really, I’d expect it to take around 1.7 times as long, but I figured 2x would be close enough that I wouldn’t worry about it. But 5-10 times longer. . . Seems like something must be wrong! Regardless, it appears to be an issue only in that one scene. Other scenes render as expected, so it’s probably a moot point now that I’ve finished with that one.

But I was hoping that someone out there might have tips on how to find the bottleneck when rendering. Like a software tool that helps you see heavy hard drive use or things like that. Or if there are things to look for in log files that would indicate the source of the issue.