sysctl: dev.cpu.0.freq: Device busy (cpufreq p4tcc / RELENG_6)

[Nate Lawson]

I'll approve a commit if you send me a patch.  Add something like this 
to the SYSCTL VARIABLES section:

The frequency cannot be changed if TSC is in use as the timecounter. 
This is because the timecounter system needs to use a source that has a 
constant rate.  The timecounter source can be changed with the 
kern.timecounter.hardware sysctl.

Marcus Alves Grando wrote:
> Well, works. Thanks. It's possible to printf some message about this if 
> kern.timecounter.hardware != ACPI-fast? Or add message in cpufreq(4)?
> 
> Thanks
> 
> Nate Lawson wrote:
>> Marcus Alves Grando wrote:
>>> I have problems in cpufreq in RELENG_6 (today).
>>>
>>> I try to set another frequency in my laptop and get this error:
>>>
>>> # sysctl dev.cpu.0.freq=250
>>> dev.cpu.0.freq: 2000
>>> sysctl: dev.cpu.0.freq: Device busy
>>>
>>> Timecounter "TSC" frequency 1995011972 Hz quality 800
>>> Timecounters tick every 1.000 msec
>>
>> Try setting your timecounter to acpi or i8254 (not TSC):
>>
>> sysctl kern.timecounter.hardware="acpi"
>>
>> Without complicated recalibration code (which no one has written yet), 
>> we can't base our system time off the TSC counter when cpufreq is 
>> changing it.
>>
> 


-- 
Nate