Pentium-M (Centrino): no power saved?

Pentium-M (Centrino): no power saved?

[Jan Rychter]

Hmm. I'm puzzled. I've just done a checkout of the latest CVS version of
cpufreq for 2.4, applied it to a 2.4.22 kernel and tried the thing out
on a Toshiba SS7/290LNKW laptop.

The speedstep-centrino module loads happily and tells me I have a 900MHz
Pentium-M. (this is a family 6 model 9 stepping 5 CPU).

I've tried echo "0%100%powersave" > /proc/cpufreq 
  and 
 echo "0%50%powersave" > /proc/cpufreq

and much to my surprise, even though /proc/cpufreq echoes my changes, I
can see no resulting changes in power consumption as reported by ACPI
battery proc entry.

Other things make a difference: whether the system is able to use C3,
display brightness, wireless card, etc. But changing the cpufreq entry
doesn't seem to do anything.

Am I doing something wrong?

--J.

Re: Pentium-M (Centrino): no power saved?

[Bas Mevissen]

Jan Rychter wrote:
> 
> I've tried echo "0%100%powersave" > /proc/cpufreq 
>   and 
>  echo "0%50%powersave" > /proc/cpufreq
> 
> and much to my surprise, even though /proc/cpufreq echoes my changes, I
> can see no resulting changes in power consumption as reported by ACPI
> battery proc entry.
> 

The line should read echo "0%0%100%userspace" >/proc/cpufreq to get 
manal control over the speed.
Then select the speed by doing

cat /proc/sys/cpu/0/speed-min > /proc/sys/cpu/0/speed

or

cat /proc/sys/cpu/0/speed-max > /proc/sys/cpu/0/speed

powersave will only change speed when you connect or disconnect AC power.

Bas.

Re: Pentium-M (Centrino): no power saved?

[Mattia Dongili]

On Fri, Sep 19, 2003 at 10:24:21AM +0200, Bas Mevissen wrote:
> Jan Rychter wrote:
> >
> >I've tried echo "0%100%powersave" > /proc/cpufreq 
> >  and 
> > echo "0%50%powersave" > /proc/cpufreq
> >
> >and much to my surprise, even though /proc/cpufreq echoes my changes, I
> >can see no resulting changes in power consumption as reported by ACPI
> >battery proc entry.
> >
> 
> The line should read echo "0%0%100%userspace" >/proc/cpufreq to get 
[...]
> powersave will only change speed when you connect or disconnect AC power.

AFAIK powersave statically sets the cpu at the minimum allowed (0% in
OP's case), while performance sets to the maximum allowed.

In this case there aren't changes because the speed/voltage is 0% of
full speed both in 

0%100%powersave

and 

0%50%powersave

correct?

try the same with performance and see if there is some changes in
/proc/cpuinfo, /proc/acpi/battery/.../state

bye
-- 
mattia
:wq!

Re: Pentium-M (Centrino): no power saved?

[Bas Mevissen]

Mattia Dongili wrote:

> 
> AFAIK powersave statically sets the cpu at the minimum allowed (0% in
> OP's case), while performance sets to the maximum allowed.
> 

Ah, you are right. It's documented at 
<http://cvs.arm.linux.org.uk/cgi/viewcvs.cgi/cpufreq/linux/Documentation/cpufreq/governors.txt?rev=1.1&only_with_tag=LINUX_2_4&content-type=text/vnd.viewcvs-markup>

Bas.

Re: Pentium-M (Centrino): no power saved?

[Bas Mevissen]

Jan Rychter wrote:
> 
> and much to my surprise, even though /proc/cpufreq echoes my changes, I
> can see no resulting changes in power consumption as reported by ACPI
> battery proc entry.
> 

Can you verify the CPU speed with the bogomips userland utility? Or 
something else that gives a CPU-only performance impression.

Bas.

Re: Pentium-M (Centrino): no power saved?

[Ducrot Bruno]

On Thu, Sep 18, 2003 at 07:09:27PM -0700, Jan Rychter wrote:
> Hmm. I'm puzzled. I've just done a checkout of the latest CVS version of
> cpufreq for 2.4, applied it to a 2.4.22 kernel and tried the thing out
> on a Toshiba SS7/290LNKW laptop.
> 
> The speedstep-centrino module loads happily and tells me I have a 900MHz
> Pentium-M. (this is a family 6 model 9 stepping 5 CPU).
> 
> I've tried echo "0%100%powersave" > /proc/cpufreq 
>   and 
>  echo "0%50%powersave" > /proc/cpufreq
> 
> and much to my surprise, even though /proc/cpufreq echoes my changes, I
> can see no resulting changes in power consumption as reported by ACPI
> battery proc entry.
> 
> Other things make a difference: whether the system is able to use C3,
> display brightness, wireless card, etc. But changing the cpufreq entry
> doesn't seem to do anything.
> 

The two use a different API for their stuff.  You just have to
chose cpufreq (of course!) or ACPI performance states.  Not the 2 at
the same time.

Next, doing
echo "0%100%powersave" > /proc/cpufreq
echo "0%50%powersave" > /proc/cpufreq

powersave governor will chose the lowest frequency available for your
cpu (in the limit you specified).  In both case, you have chosen
the lowest frequency.

Please note also that if really you use the ACPI perf, and you have
a thermal zone with passive cooling, then the performance stuff (from
the thermal zone) may confuse cpufreq.

*BLINK* This is not the case for 2.6, which is well designed in
that regard *BLINK*

-- 
Ducrot Bruno

--  Which is worse:  ignorance or apathy?
--  Don't know.  Don't care.

Re: Pentium-M (Centrino): no power saved?

[Toula Michael]

>
>
> powersave will only change speed when you connect or disconnect AC power.


Really ? I thougt powersave allways choose the lowest supported 
frequency (policy->min) no matter if the AC power is connect or not. A 
look at      
static int __cpufreq_governor(struct cpufreq_policy *policy, unsigned 
int event)
{
...
}
in the file cpufreq.c (line 354) confirme that...
Do I miss something ?

Oh, and before I forget, what's the difference between policy and governor ?

Thx in advance
Mike

Re: Pentium-M (Centrino): no power saved?

[Jan Rychter]

>>>>> "Bas" == Bas Mevissen <ml@basmevissen.nl> writes:
 Bas> Jan Rychter wrote:
 >> and much to my surprise, even though /proc/cpufreq echoes my
 >> changes, I can see no resulting changes in power consumption as
 >> reported by ACPI battery proc entry.

 Bas> Can you verify the CPU speed with the bogomips userland utility? 
 Bas> Or something else that gives a CPU-only performance impression.

Ok, I haven't actually verified the CPU speed as reported by bogomips,
but I've done some power consumption measurements. This is on a Toshiba
S7/290LNKW, which has a 900MHz Pentium-M, the machine had its HDD spun
down, no wi-fi or other networking, display set to max brightness and
was otherwise idle.

11048mW 900MHz, C2 only
10560mW 600MHz, C2 only

9306mW 900MHz, C3 allowed
9306mW 600MHz, C3 allowed

So, it seems that changing the frequency actually buys very little if
you're stuck in C2 (about 0.5W) and exactly NOTHING if the machine is
idle and can use C3.

FYI, a good way to get the machine not to use C3 is to plug in an USB
device. Or just use usb-uhci, which immediately disallows C3 states.

An unscientific comparison with my old Sharp Mebius Pentium3M-based,
750MHz, shows that the old machine has actually better idle performance,
with 8750mW at max display, no HDD, and speedstepped down to 350MHz.

Another test has shown that on the Pentium-IIIM machine it DOES make a
difference if it's speedstepped high or low. The numbers for lowest
brightness, no HDD, idle machine:
  speedstep 350MHz
  5757mW
  speedstep 750MHz
  5905mW

5757mW is BTW the absolute minimum this machine can do with the display
on :-)

The above results are rather surprising for me. Either something is
wrong, or Intel has managed to make a CPU which effectively doesn't
really need frequency scaling, because it is so good at idle
handling. But then I thought that voltage also changes along with the
frequency?

--J.

Re: Pentium-M (Centrino): no power saved?

[Bas Mevissen]

Jan Rychter wrote:

>>>>>>"Bas" == Bas Mevissen <ml@basmevissen.nl> writes:
> 
>  
> 11048mW 900MHz, C2 only
> 10560mW 600MHz, C2 only
> 
> 9306mW 900MHz, C3 allowed
> 9306mW 600MHz, C3 allowed
> 
> So, it seems that changing the frequency actually buys very little if
> you're stuck in C2 (about 0.5W) and exactly NOTHING if the machine is
> idle and can use C3.
> 

Do you measure this from the ACPI baatery output? I still suspect that 
your CPU is only running at low speed all the time. So please boot with 
AC adapter in and check /proc/cpuinfo and reboot without AC adapter and 
check again. In the meantime, get bogomips as it is worthless as a 
benchmark, but usefull to compare :-)

Bas.

Re: Pentium-M (Centrino): no power saved?

[Jan Rychter]

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> >>>>>>"Bas" == Bas Mevissen <ml@basmevissen.nl> writes:
> Jan Rychter wrote:
> >  11048mW 900MHz, C2 only
> > 10560mW 600MHz, C2 only
> > 9306mW 900MHz, C3 allowed
> > 9306mW 600MHz, C3 allowed
> > So, it seems that changing the frequency actually buys very little if
> > you're stuck in C2 (about 0.5W) and exactly NOTHING if the machine is
> > idle and can use C3.
> >
> 
> Do you measure this from the ACPI baatery output? 

Yes.

> I still suspect that your CPU is only running at low speed all the
> time. So please boot with AC adapter in and check /proc/cpuinfo and
> reboot without AC adapter and check again. In the meantime, get
> bogomips as it is worthless as a benchmark, but usefull to compare :-)

No, I have verified this (with bogomips) and the above results are
true. The CPU does indeed slow down properly as directed by
cpufreq. Also, in my case connecting and disconnecting the AC adapter
doesn't change the CPU speed.

So, the results still hold -- and it seems it simply doesn't make much
sense to slow down a Pentium-M, unless you really keep the CPU busy?

--J.

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Re: Pentium-M (Centrino): no power saved?

[Bas Mevissen]

Jan Rychter wrote:
>>>>>>>>"Bas" == Bas Mevissen <ml@basmevissen.nl> writes:
>>
>>
>>Do you measure this from the ACPI battery output? 
> 
> Yes.
> 

OK. Do you know of a way to see the power usage when on AC-adapter? I'm 
wondering if there isn't something in the on-board power circuit to see 
the actual power usage of the PC or just CPU or motherboard.

> No, I have verified this (with bogomips) and the above results are
> true. The CPU does indeed slow down properly as directed by
> cpufreq. Also, in my case connecting and disconnecting the AC adapter
> doesn't change the CPU speed.
> 
> So, the results still hold -- and it seems it simply doesn't make much
> sense to slow down a Pentium-M, unless you really keep the CPU busy?
> 

Very interesting conclusion. It could mean three things:
1) The internal power management of the Pentium-M (when using APM or 
ACPI idle calls) is very good
2) The speedstepping of the Pentium-M doesn't bring enough
3) We are interpreting something wrong :-)

 From your conclusions, 1) would be the most reasonable and most 
favourable result.

Bas.