10.0-BETA2: LAPIC event timer and C2 c-state -> abnormal high load

[Jean-Sébastien Pédron]

Hello!

I partially upgraded my workstation from 9.2-RELEASE-p1 to 10.0-BETA2 
using freebsd-update. Partially because I only performed the first pass 
(installing the kernel and rebooting).

After the boot, the average load was around 5, with no activity on the 
computer. I tried again by disabling all services in rc.conf and 
rebooted: same load.

Other symptoms are:
     o  The display (syscons) is only redrawn when hitting random keys
        on a PS/2 or USB keyboard.
     o  When all services are disabled (even NIC is not configured), the
        computer isn't able to boot or shutdown in a reasonable time
        without hitting the keyboard too (I guess to generate some
        interrupts).

The chosen event timer is different between 9.2 and 10.0:

9.2:
kern.eventtimer.timer: HPET
kern.eventtimer.choice: HPET(450) HPET1(440) HPET2(440) HPET3(440) 
LAPIC(400) i8254(100) RTC(0)

10.0:
kern.eventtimer.timer: LAPIC
kern.eventtimer.choice: LAPIC(400) HPET(350) HPET1(340) HPET2(340) 
HPET3(340) i8254(100) RTC(0)

I have hw.acpi.cpu.cx_lowest=C2 in sysctl.conf.

I tested the following combinations:
     o  HPET  + cx_lowest=C1: normal load, computer responsive
     o  HPET  + cx_lowest=C2: normal load, computer responsive
     o  LAPIC + cx_lowest=C1: normal load, computer responsive
     o  LAPIC + cx_lowest=C2: high load /!\

Can someone help me track the problem down? :)

Thanks!

-- 
Jean-Sébastien Pédron