CPU frequency doesn't drop below 1200MHz (like it used to)

[Kimmo Paasiala]

On Fri, May 22, 2015 at 8:19 PM, Ian Smith <smithi at nimnet.asn.au> wrote:
> On Fri, 22 May 2015 16:28:49 +0300, Kimmo Paasiala wrote:
>  > On Fri, May 22, 2015 at 10:42 AM, Ivan Klymenko <fidaj at ukr.net> wrote:
>> Fri, 22 May 2015 09:33:15 +0200
>> Nikos Vassiliadis <nvass at gmx.com> яяяяяяяяяяяяяя:
>>
>>> Hi,
>>>
>>> I just noticed that my CPU's frequency doesn't support dropping
>>> below 1200MHz. It used to be able to go down to 150MHz, if I am
>>> not mistaken. I'd like it to go down to 600MHz via powerd, like
>>> it used to go. This is a month's old 10-STABLE.
>>>
>>> > [nik at moby ~]$ sysctl dev.cpu.0.freq_levels
>>> > dev.cpu.0.freq_levels: 2400/35000 2300/32872 2200/31127 2100/29417
>>> > 2000/27740 1900/26096 1800/24490 1700/22588 1600/21045 1500/19534
>>> > 1400/18055 1300/16611 1200/15194
>>>
>>> This is the CPU:
>>>  > hw.model: Intel(R) Core(TM) i3-3110M CPU @ 2.40GHz
>>>
>>> Thanks in advance for any ideas,
>>> Nikos
>>
>> Try changing the options in /boot/device.hints
>> hint.acpi_throttle.0.disabled="0"
>> hint.p4tcc.0.disabled="0"
>
>  > Thanks, those also fixed powerd(8) for me that stopped working after
>  > upgrading to stable/10 from releng/10.1. Why are those setting
>  > suddenly needed now?
>  >
>  > -Kimmo
>
> Looks like the changes to these two hints, now defaulting to 1,
> committed to -head some months ago has been merged to stable/10.
>
> Can you say exactly in what way powerd stopped working then?

Powerd(8) complained (excerpt from dmesg -a):

Starting powerd.
powerd: no cpufreq(4) support -- aborting: No such file or directory
/etc/rc: WARNING: failed to start powerd

Putting those two settings in loader.conf and rebooting fixed the
problem and powerd started working again apparently because cpufreq(4)
device was available again.

-Kimmo

>
> Except that the minimum frequency that may be set with powerd's -m
> switch will be higher without p4tcc (or acpi_throttle) running, this
> change shouldn't hurt powerd; if anything it should be more efficient,
> as the lower p4tcc-generated frequencies don't save much if any power.
>
> If you compare dev.cpu.0.freq_levels, as above, both before and after
> booting with the changed hints, you can see the ones due to p4tcc's use
> of subfrequencies with factors of 1/8 to 7/8 of some base freq, but the
> power use in milliWatts provided for these seems largely ficticious.
>
> On my Lenovo X200, Core2Duo 2.4GHz, idling on battery at 800MHz (minimum
> EST freq) or at 100MHz using p4tcc draws almost exactly the same power,
> about 7.6W measured from the battery - but responsiveness as performance
> is required is a great deal better using just the base EST freqs; YMMV.
>
> This generally gets discussed on the freebsd-mobile and freebsd-acpi
> lists; not sure if a deeper discussion of issues is warranted here.
>
> cheers, Ian