powerd and increase in energy need

[Kevin Oberman]

On Wed, Mar 21, 2012 at 12:41 AM, Matthias Gamsjager
<mgamsjager at gmail.com> wrote:
> On Wed, Mar 21, 2012 at 1:00 AM, John <john at theusgroup.com> wrote:
>
>> >my zfs nas has an Asus p5e motherboard (x38 chip) and an intel q9300 (quad
>> >core 2,5Ghz) processor with all the energy save setting enabled in the
>> >bios. Today I connected the power cord to a voltcraft energy meter to see
>> >how much energy the whole system needs in idle mode.
>> >
>> >I found out that with powerd running the cpu get clocked down to 499 mhz
>> >with is nice. The funny thing is that this doesn't decrease the amount of
>> >watts the machine need. 2,5ghz or 499mhz doen't matter at all. It gets
>> even
>> >funnier. With powerd running the systems actually needs 4 watts more then
>> >without powerd running.
>> >
>> >Isn't the whole point of powerd to to decease the energy needs of a
>> >machine? or is it utterly broken with this cpu generation?
>>
>> Powerd does decrease energy on my more modern hardware. This machine is
>> used
>> for backups and is idle much of the time. It runs Freebsd 8.3-Prerelease
>> with
>> the turbo-boost patch on an i5-650 in an intel DH55HC motherboard.
>>
>> The following power measurements were made with a Kill-A-Watt meter.
>>
>> 91w while doing a compile, dev.cpu.0.freq: 3193 (turbo boost enabled)
>> 81w compile complete, disks quiet, top reports between 99.9 and 100% idle
>>        dev.cpu.0.freq: 3193
>> 71w idle for several seconds, powerd running in hiadaptive mode,
>>        dev.cpu.0.freq: 1197
>>
>>
>> sysctl dev.cpu |grep cx
>> dev.cpu.0.cx_supported: C1/3 C2/205 C3/245
>> dev.cpu.0.cx_lowest: C2
>> dev.cpu.0.cx_usage: 100.00% 0.00% 0.00% last 259us
>>
>> sysctl dev.cpu |grep freq                                           ~
>> dev.cpu.0.freq: 1197
>> dev.cpu.0.freq_levels: 3193/9875 3192/9125 3059/8250 2926/7500 2793/6875
>> 2660/6250 2527/5750 2394/5250 2261/4750 1197/2750
>>
>> /etc/rc.conf
>> powerd_flags="-n hadp"
>> performance_cx_lowest="C2"
>> economy_cx_lowest="C2"
>> performance_cpu_freq="HIGH"
>>
>> John Theus
>> TheUs Group
>> TheUsGroup.com
>>
>
> I will give these setting a try thx..

If you are trying to reduce power consumption, why are you limiting Cx
states to C2 (which save little) and not C3 (which will save a LOT of
power when the CPU is not heavily loaded).

If it is due to the system hanging, it is almost certainly because you
have throttling enabled. Throttling, either by the use of TCC (also
called P4TCC) or the older, externally implemented throttling
mechanism, is a BAD BAD THING! I have complained for years about it
being the default. It is intended for thermal control, not power
management. The power savings will be negligible and, in combination
with deep sleep modes (Cx > 2) can and do result in the CPU going into
deep sleep and never waking up.

You can (and should) disable them in /boot/loader.conf with:
# Disable CPU throttling
hint.p4tcc.0.disabled=1
hint.acpi_throttle.0.disabled=1

This should greatly reduce the large number of "frequencies"
available, but they will be the ones provided by EST.which really do
reduce power consumption. (I put frequencies in quotation marks
because throttling does not really change the clock speed. It simply
skips 'N' of every 8 clock cycles. Still, compared to C3 and higher,
EST is a minor power savings.

Just following the recommendations on the power management web page is
the way to go.
-- 
R. Kevin Oberman, Network Engineer
E-mail: kob6558 at gmail.com