cpufreq & enhanced speedstep

Rui Paulo rpaulo at fnop.net
Tue May 15 11:05:01 UTC 2007


At Tue, 15 May 2007 12:47:18 +0200,
Harald Schmalzbauer wrote:
> 
> Am Dienstag, 15. Mai 2007 schrieb Rui Paulo:
> > At Mon, 14 May 2007 23:48:07 +0200,
> >
> > Harald Schmalzbauer wrote:
> [...]
> > > I have a E6600 core2 and tried to reduce power dissipation by enabling
> > > some speedstep technology.
> > > acpi_perf seems to work since dev.cpu.freq shows 800 (possible
> > > 2400/1600/800) and goes up while compiling, but I frequently get the
> > > following errors:
> > >
> > > kernel: acpi_perf0: Px transition to 1600 failed
> > > kernel: acpi_perf0: set freq failed, err 6
> >
> > I don't really know why it fails..
> 
> With acpi_throttle and p4tcc disabled, like you advised, this
> message doesn't occur any more.
> But I only have two possible speed steps, 2400 and 1600. But it's switching 
> smoothly between them, atm. I don't have a power meter handy, so I can't see 
> if it really works (and saves power).

I have a driver to gather the temperature reading of the CPU.
If the temperature drops when you've enabled powerd, then it's most
likely working.
(Check my message "MacBook patches" if you wanna try it out)

> But in any case, the Watt values (dev.cpu.0.freq_levels: 2400/88000 
> 1600/56000) are wrong for my core2 CPU.
> Where does acpi_perf get them from? Ok, form est (since without
> cpufreq loaded  
> the values are /-1) but are they readable from any registers or are
> they hard  
> coded according to the CPU type or are they in any table in the (acpi) BIOS?

It gets the values from ACPI methods.

--
Rui Paulo


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