How to enable CPU turbo mode on FreeBSD?

Pierre-Luc Drouin pldrouin at
Fri Sep 11 15:45:49 UTC 2009

John Baldwin wrote:
> 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, 
> FreeBD 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.
Sorry I am not sure exactly what you are referring to. Do you mean that 
I need to enable C2/C3 states in order to have the correct max CPU freq 
value displayed at boot time/in sysctl, or you mean that I need these 
states in order to be able to use the Turbo Mode at all? Right now in 
the BIOS I had the following features disabled to test the overclocking 
(I was following what is recommended to do for Windows users to run 
stress tests):

-Intel SpeedStep: Use this function to enable the Intel SpeedStep 
technology (EIST)
-CxE Function: This function allows you to select the lowest C state 
supported according as CPU and MB. The options are Auto, Disabled, C1, 
C1E, C3 and C6


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