Problems with hw.acpi.cpu.cx_lowest=C2 (Re: cvs commit: src/etc/defaults rc.conf)

Nate Lawson nate at
Mon Mar 13 17:03:59 UTC 2006

Kris Kennaway wrote:
> On Sun, Jan 29, 2006 at 01:30:07AM -0500, Kris Kennaway wrote:
>> On Sat, Jan 28, 2006 at 10:17:47PM -0800, Nate Lawson wrote:
>>> Kris Kennaway wrote:
>>>> On Sun, Jan 29, 2006 at 01:06:54AM -0500, Kris Kennaway wrote:
>>>>> On Sun, Jan 29, 2006 at 05:51:58AM +0000, Nate Lawson wrote:
>>>>>> njl         2006-01-29 05:51:58 UTC
>>>>>> FreeBSD src repository
>>>>>> Modified files:
>>>>>>   etc/defaults         rc.conf 
>>>>>> Log:
>>>>>> Enable the lowest Cx state by default.  This will save power and we have
>>>>>> had enough testing of acpi_cpu to know this is stable now.
>>>>> On my desktop system (running RELENG_6 though), setting
>>>>> hw.acpi.cpu.cx_lowest=C0 causes atrocious performance.  Is it broken
>>>>> in 6.x?
>>>> C2, sorry.
>>> Ah, C0 should be disallowed already I thought (try it).
>>> As for C2, I MFCd a patch to acpi_cpu.c in November that should prevent 
>>> this (  Do you get a printf on console?
>> This might be it: turns out I never rebooted to the newer kernel I
>> built earlier this month, and I am still running a kernel from Nov 6.
>> I'll get back to you.
> I finally managed to test this in RELENG_6.  The system performance is
> not obviously bad, but sound playback is distorted (e.g. the 'bell' in
> KDE is much higher pitched than it should be, and on the console it is
> low pitched and lasting about 3 seconds).  Nothing is logged on
> console.
> There may be other problems that I didn't notice right away, but the
> sound problems were enough to make me turn it off again.

Are you sure that's the cause?  (Does setting cx_lowest to C1 fix it?) 
Can you send the output of sysctl hw.acpi so we can see how often each 
cx type is being run?


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