Processor C states and USB problem

[mike-Z92qn3yYq0hWk0Htik3J/w@public.gmane.org]

Recently I had problems with my network card and ACPI (see earlier posts for 
the problem and solution) so I thought I'd take a closer look at ACPI on 
this notebook (Acer Travelmate 800). 

Looking at the proc entries for the processor I saw the following. 

active state:            C3
default state:           C1
bus master activity:     80070020
states:
   C1:                  promotion[C2] demotion[--] latency[000] 
usage[00000010]
   C2:                  promotion[C3] demotion[C1] 
latency[001]usage[01077887]
  *C3:                  promotion[--] demotion[C2] latency[085] 
usage[00083507] 

This looked pretty normal to me, apart from the fact that the processor was 
spending a lot of time in C3 although the notebook was idle. 

Now I plugged in my USB mouse. 

cat /proc/acpi/processor/CPU0/power
active state:            C2
default state:           C1
bus master activity:     ffffffff <---- USB is active
states:
   C1:                  promotion[C2] demotion[--] latency[000] 
usage[00000010]
  *C2:                  promotion[C3] demotion[C1] 
latency[001]usage[00871647]
   C3:                  promotion[--] demotion[C2] latency[085] 
usage[00077386] 

The processor never left the C2 state.
After unplugging the mouse "bus master activity" showed normal values again. 

Now for my two questions: 

1.) Is it normal for the notebook to spend so much time in C3, even if it is 
idle? 

2.) Why is an USB device screwing up the bus master activity, resulting in 
the processor never leaving C2? 


/Michael 




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