Keep Your Scanners Peeled (CPU throttling fun with SystemUIServer and TWAINBridge)

Lion users: Have you encountered weird CPU spikes that cause your Mac to slow to a crawl?

Do you have a Canon scanner?

If you said “yes” to both, chances are pretty strong that your Canon scanner is causing the CPU spike, by continuously throttling Lion’s SystemUIServer and TWAINBridge processes.

The problem manifests itself after your Mac has been on for a day or two, and is temporarily resolved by rebooting your Mac. After an exhaustive amount of troubleshooting, Googling, and other assorted voodoo, I came across a very helpful thread in Apple’s Discussion forums that solved my problem. No word as of yet if an update to fix the issue is on its way.

Pretty annoying, but the workaround to the problem (for now) is unplugging the scanner when it’s not being used.

CPU usage before unplugging the Canon scanner:

CPU usage after unplugging the scanner:

(The CPU meters shown in the screenshots above come from iStat 3 which I reviewed last year.)

-Krishna

Update: Later this afternoon, I plugged the Canon scanner directly into the Mac Pro’s front USB ports and the CPU spikes did not return. I’ll keep an eye on this over the next few days. My suspicions have shifted towards my Kensington 7-port USB hub, which was initially connecting the scanner to the computer.