Observed problem:

When I plug my Presonus Firebox into my PowerBook G4 running OS X 10.4.9, my CPU usage shoots up (even without any audio or MIDI being active). In Activity Monitor, kernel_task takes up 15-25% of the CPU. As soon as I unplug the device, the CPU usage returns to normal and kernel_task returns to 0.5-1% of the CPU.

We were able to verify that the same problem happens on a MacBook Pro running 10.4.9, and that it also happens on both machines running earlier versions of 10.4. Strangely enough, on a new, top-of-the-line MacBook Pro, it uses the exact same percent of the CPU (20%) as on my 4-year-old 1Ghz PowerBook G4.

The problem does not happen on my PowerBook when running 10.3.7.


From Presonus:

There is a phenomenon called 'ghost spiking' which may be what your client is seeing.  Core Audio is on a scan cycle for firewire audio devices, when the Core Audio scan coincides with a processor work function, there is a spike (about 20%).  This spike, however, is not a true drain on system performance.  As long as the spiking isn't coinciding with an audio drop out or popping/clicking noise, it's not really something to be concerned about.  I know that Apple is aware of this issue and each version of 10.4 does see a marked improvement.