Why does the Finder run at such a low process priority? I'm at a bit of a loss about this.
I'm running a big import in aperture, and it's causing my system to slow down to a complete crawl, basically rendering it unusable for anything, even browsing the web. Since this seems a bit unnatural, I spent a little time looking around.

Running ps -Al shows that, apparently by default, the Dock, Finder, and SystemUIServer all seem to run at a priority far lower then userland applications. While user applications typically have a priority of 33, the Dock, Finder, etc have a priority of 53.

The end result, is ANY processor intensive task completely clobbers the UI, and renders the system unusable until it finishes.

Anyways, using renice -20 -p &lt;prid&gt; bumps them up to the same priority as the rest of the userland UI, and results in not having to wait 1-3 seconds (!) for the UI to respond to something as simple as a mouse click.

Thad said, I have two questions:
Is there any reason I shouldn't be altering the thread priority of the finder like this?
Is there any way to make the priority change persistent, e.g. so it stays that way after reboot.
I'm not sure anyone short of Apple's own developers would be able to answer this question, Finder's inner secrets are their domain. If you do think there are some noticeable lag problems with the UI you might want to submit a bug report to Apple about it.

Judging from the sound of things (processes intentionally taking up all resources) this is a bit of an edge case for memory management. I've yet to see a system perform at their best without somewhere around 10-20% resources free, as a buffering aid.

Just curious, what are these processes you're running?