CPU throttling & power conservation expectations

CPU throttling & power conservation expectations

[nate]

I've been on this list for about a week and have only seen
1 email from a human, wonder if anyone else is out there.

Anyways I had a quick question on using cpufreq to reduce
power usage by clocking the CPUs down.

I tested it out on a selection of about a half dozen
HP DL320G4s running Pentium D 3Ghz, which appear to be
the '925' model.

kernels were primarily 2.6.17-1.2142_FC4smp. I used the
p4-clockmod and cpufreq_powersave modules. cpufreq-info
reported that the cpus were successfully clocked down to
the ~300-400mhz range(forgot exactly what speed).

I expected at least some reduction in power usage, but
to my suprise my intelligent power strips did not report
even 0.1 amps(@110V) worth of power savings.

I did the same on a selection of HP DL360G4p systems
with Xeon 3.0-3.6Ghz, with similar results, no measurable
drop in power utilization, despite cpufreq saying that
the cpus were clocked down.

I was just wondering if this mirrors other people's
experiences or if something is broken.

I do notice of course that power usage goes up if I run
high loads on the systems. I was just expecting that
clocking a cpu from 3+Ghz down to sub 500mhz would show
some measurable amount of power savings, and if not then
there doesn't seem to be a lot of point in supporting
these CPUs.

We intend to migrate to a newer distribution soon and I can
try again on that kernel, but these systems are fairly
old as-is(especially the DL360G4s).

thanks!

nate

RE: CPU throttling & power conservation expectations

[Langsdorf, Mark]

> kernels were primarily 2.6.17-1.2142_FC4smp. I used the
> p4-clockmod and cpufreq_powersave modules. cpufreq-info
> reported that the cpus were successfully clocked down to
> the ~300-400mhz range(forgot exactly what speed).

p4-clockmod throttles the clock frequency but doesn't
adjust the processor voltage.  You should be using the
speedstep-centrino or acpi drivers.
 
> I expected at least some reduction in power usage, but
> to my suprise my intelligent power strips did not report
> even 0.1 amps(@110V) worth of power savings.

Shouldn't power utilization be measured in watts, not
amps?  My electrical engineering classes were a long
time ago.

I've observed a dual-processor Opteron system pulling 
150 watts from the wall at full frequency and voltage,
and then dropping to 75 watts at a lower pstate.  We
did this as a demo at Linux World Expo in 2004.

Also see Paul Devriendt's paper on the same:
http://www.linuxsymposium.org/proceedings/LinuxSymposium2004_V1.pdf

-Mark Langsdorf
Operating System Research Center
AMD, Inc.

RE: CPU throttling & power conservation expectations

[nate]

Langsdorf, Mark said:
>> kernels were primarily 2.6.17-1.2142_FC4smp. I used the
>> p4-clockmod and cpufreq_powersave modules. cpufreq-info
>> reported that the cpus were successfully clocked down to
>> the ~300-400mhz range(forgot exactly what speed).
>
> p4-clockmod throttles the clock frequency but doesn't
> adjust the processor voltage.  You should be using the
> speedstep-centrino or acpi drivers.
>

ok, that would explain some then, those other drivers
wouldn't load, must not be compatible.

[root@prod-admin-2 cpufreq]# modprobe acpi-cpufreq
FATAL: Error inserting acpi_cpufreq
(/lib/modules/2.6.17-1.2142_FC4smp/kernel/arch/i386/kernel/cpu/cpufreq/acpi-cpufreq.ko):
Device or resource busy

[root@prod-admin-2 i386]# grep -i acpi /boot/config-2.6.17-1.2142_FC4smp
# Power management options (ACPI, APM)
# ACPI (Advanced Configuration and Power Interface) Support
CONFIG_ACPI=y
[..]



>> I expected at least some reduction in power usage, but
>> to my suprise my intelligent power strips did not report
>> even 0.1 amps(@110V) worth of power savings.
>
> Shouldn't power utilization be measured in watts, not
> amps?  My electrical engineering classes were a long
> time ago.

Well, I think you know what I meant :) it's easy enough
to convert amps+volts to watts.. My power strips measure
draw in amps. My newer HP gear supports retrieving power
usage via the management port, though the versions of
the cpufreq drivers in the kernel don't run on those
systems either.

>
> I've observed a dual-processor Opteron system pulling
> 150 watts from the wall at full frequency and voltage,
> and then dropping to 75 watts at a lower pstate.  We
> did this as a demo at Linux World Expo in 2004.
>
> Also see Paul Devriendt's paper on the same:
> http://www.linuxsymposium.org/proceedings/LinuxSymposium2004_V1.pdf

thanks a bunch for the quick response I'll check that
PDF out too. I'll dig into it more when we go to the
newer distribution/kernel.

nate

RE: CPU throttling & power conservation expectations

[Pallipadi, Venkatesh]

 

>-----Original Message-----
>From: cpufreq-bounces@lists.linux.org.uk 
>[mailto:cpufreq-bounces@lists.linux.org.uk] On Behalf Of nate
>Sent: Tuesday, March 27, 2007 2:27 PM
>To: cpufreq@lists.linux.org.uk
>Subject: RE: CPU throttling & power conservation expectations
>
>Langsdorf, Mark said:
>>> kernels were primarily 2.6.17-1.2142_FC4smp. I used the
>>> p4-clockmod and cpufreq_powersave modules. cpufreq-info
>>> reported that the cpus were successfully clocked down to
>>> the ~300-400mhz range(forgot exactly what speed).
>>
>> p4-clockmod throttles the clock frequency but doesn't
>> adjust the processor voltage.  You should be using the
>> speedstep-centrino or acpi drivers.
>>
>
>ok, that would explain some then, those other drivers
>wouldn't load, must not be compatible.
>
>[root@prod-admin-2 cpufreq]# modprobe acpi-cpufreq
>FATAL: Error inserting acpi_cpufreq
>(/lib/modules/2.6.17-1.2142_FC4smp/kernel/arch/i386/kernel/cpu/
>cpufreq/acpi-cpufreq.ko):
>Device or resource busy
>
>[root@prod-admin-2 i386]# grep -i acpi 
>/boot/config-2.6.17-1.2142_FC4smp
># Power management options (ACPI, APM)
># ACPI (Advanced Configuration and Power Interface) Support
>CONFIG_ACPI=y
>[..]
>

Does your processors support Enhanced Speedstep feature (does
/proc/cpuinfo flags contain 'est')?

If yes, also check whether your BIOS is enabling Enhanced speedstep
correctly and whether there are any options in BIOS to enable.

Thanks,
Venki

RE: CPU throttling & power conservation expectations

[nate]

Pallipadi, Venkatesh said:

> Does your processors support Enhanced Speedstep feature (does
> /proc/cpuinfo flags contain 'est')?

Looks like my DL320s do (Pentium D), but I don't see the flag
on the DL360G4ps (Xeon ~3Ghz). And upon checking I was able to
load the acpi-cpufreq module on the DL320 without any errors.


> If yes, also check whether your BIOS is enabling Enhanced speedstep
> correctly and whether there are any options in BIOS to enable.

The HP bios isn't big on options, I'll take a look but I don't
recall anything talking about speedstep in the bios, though they
may have their own terminology for it.

HP does have a 'dynamic power saving' option on the DL320 BIOS
(I think it is related to the voltage regulator):

http://h18013.www1.hp.com/products/servers/management/ilo/power-regulator.html

"HP Dynamic Power Savings Mode: Automatically varies processor
speed and power usage based on processor utilization. Allows
reducing overall power consumption with little or no impact
to performance. Does not require OS support."

Which I tried to enable, but the BIOS spit out an error upon
reboot saying that option wasn't supported in my specific
processor configuration despite their online docs seemingly saying
it is supported(running latest bios rev from 11/2006).

I'll run another test on the DL320 test systems with the acpi
module loaded and see if it shows a noticable power use reduction.

thanks a bunch!

nate

Units of measurement [was: Re: CPU throttling & power conservation expectations]

[Francesco Poli]

[-- Attachment #1.1: Type: text/plain, Size: 971 bytes --]

On Tue, 27 Mar 2007 15:54:30 -0500 Langsdorf, Mark wrote:

[...]
> Shouldn't power utilization be measured in watts, not
> amps?  My electrical engineering classes were a long
> time ago.

Definitely: adopting the International System of Units (SI), we have

  * the watt (symbol: W) is the SI unit of power
  * the ampere (symbol: A) is the SI unit of electric current
  * the volt (symbol: V) is the SI unit of electric potential difference

See http://www.bipm.fr/ for further details: especially
http://www.bipm.fr/en/si/si_brochure/chapter2/2-1/ampere.html
http://www.bipm.fr/en/si/si_brochure/chapter2/2-2/table3.html


Just in case yours was a serious question...  ;-) 


-- 
 http://frx.netsons.org/doc/nanodocs/etch_workstation_install.html
 Need to read a Debian etch installation walk-through?
..................................................... Francesco Poli .
 GnuPG key fpr == C979 F34B 27CE 5CD8 DC12  31B5 78F4 279B DD6D FCF4

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Re: CPU throttling & power conservation expectations

[Wes Felter]

nate wrote:

> kernels were primarily 2.6.17-1.2142_FC4smp. I used the
> p4-clockmod and cpufreq_powersave modules. cpufreq-info
> reported that the cpus were successfully clocked down to
> the ~300-400mhz range(forgot exactly what speed).
> 
> I expected at least some reduction in power usage, but
> to my suprise my intelligent power strips did not report
> even 0.1 amps(@110V) worth of power savings.

This is not too surprising; the p4-clockmod driver is mostly useless. 
When the processor is idle, most of it is clock gated (effectively 0 
MHz) anyway, so reducing the frequency makes no difference. Under high 
load p4-clockmod should reduce power a little.

Wes Felter - wesley@felter.org