How to enable CPU turbo mode on FreeBSD?

[John Baldwin]

On Thursday 10 September 2009 8:57:32 pm Pierre-Luc Drouin wrote:
> Hi,
> 
> I have an overclocked i7 920 CPU for which I have enabled Turbo Mode in 
> the BIOS (21x multiplier). The base clock is set at 190 MHz, so the CPU 
> frequency with Turbo mode activated should be 3990 MHz. However the 
> maximum value FreeBSD amd64 shows for the CPU frequency in dmesg and 
> sysctl is 3790 MHz. How can I enable the Turbo Mode?
> 
> CPU: Intel(R) Core(TM) i7 CPU         920  @ 2.67GHz (3790.52-MHz 
> K8-class CPU)
> 
> machdep.acpi_timer_freq: 3579545
> machdep.tsc_freq: 3790522507
> machdep.i8254_freq: 1193182
> dev.cpu.0.freq: 349
> dev.cpu.0.freq_levels: 2793/130000 2443/113750 2094/97500 1745/81250 
> 1396/65000 1047/48750 698/32500 349/16250

You have to enable C2/C3 sleep states (possibly in your BIOS).  However, 
FreeBSD doesn't currently handle this but so well since that will probably 
turn off the local APIC timer interrupt when the CPU is idle causing FreeBSD 
to miss clock interrupts.

-- 
John Baldwin