Event based scheduling and USB.

I updated my FreeBSD tree on laptop, to the current
as of 18 Oct.2010, it works fine with CPU C3 state enabled,

I think this is your achievement of event time scheduler,
thanks!

But when USB driver is enabled, the load average is considerablly 
high (0.6 to 1.0) if sysctl oid kern.eventtimer.periodic is set to 0.
 Then kern.eventtimer.periodic is set to 1, the load average goes
to 0 quickly as before, but almost never transit to C3.

Is this behavior expected, or something wrong?
I noticed one of usb host controller device shares HPET irq.
When I implement interrupt filter in uhci driver, the load average
goes to 0 as before.


====
% vmstat -i
interrupt                          total       rate
irq1: atkbd0                         398          2
irq9: acpi0                          408          2
irq12: psm0                            3          0
irq19: ehci1                          37          0
irq20: hpet0 uhci0                 35970        230
irq22: ehci0                           2          0
irq256: em0                            4          0
irq257: ahci0                       1692         10
Total                              38514        246
===


BTW, when USB port is enabled C3 transition rate gets lower.
I think it is likely to occur. But how can I supress power 
consumption? 

It's time to implement powertop for freebsd, isn't it?