After boot both cores run at 800 MHz, but during boot they run on 2GHz. And the hardware can't power off.
I tried cpufrequtils and got some statistics, and another boot problem... 2.0 GHz, 1.8 GHz, 1.6 GHz and 800 MHz available but the governor can only set "within 800 MHZ and 800 MHZ" cpufreq-set was able to change governor but not any frequency, and cpufrequtils caused the system to freeze during boot, so it had to go...
If I boot the system with acpi=off in grub I get a single core system running at 2 GHz.
I guess that this is APIC related, but will appreciate pointers in any direction.