How to enable CPU turbo mode on FreeBSD?

[John Baldwin]

On Friday 11 September 2009 11:46:13 am Pierre-Luc Drouin wrote:
> 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

You need to have C2/C3 enabled for it to work at all, at least on Nehalem 
processors.

-- 
John Baldwin