[ltp] how to reduce the power consumption of the X200?

[Volker Krueger]

Hi Roman,

thanks for sharing your observations!

I have observed exactly the same things as you describe on the X200s.
But I want to add the following:
My present laptop has the L9400 Core 2 Duo processor, 1.8GHz.

I ended up first using the values 21 21 2 2 for the four different
frequencies.
Then, the system froze after I started accessing the wireless card, so
that I increased to  21 21 4 4.
next, I looked at the wattage: Switching off the network adapters and
while trying to keep the system  using a constant wattage, I first
decreased the voltage slowly to 1 and then increased it to 6. The
minimum wattage was at 4(!!), and not, as expected, at the lower
numbers. Perhaps someone can confirm this?
If I remember correctly, I had 10.2W at setting 4 and 10.7W at setting 2
(measuring with powertop).
I wasn't sure if 10.2W and 10.7W is within the natural variance of the
system's power consumption, so I retried several times.

best,
vok





>   
> now, on the T61 with a Core 2 Duo 2.4GHz, things got much more complex.
> my understanding of what actually is happening deep inside in the
> hardware is limited, so i can only tell what i tried, eventhough it
> doesn't make too much sense for someone more knowledgeable. i was trying
> to use the same approach as described above for finding good voltage
> values. i think, they are called 'vids' in phc lingo, where 0
> corresponds to 700ms an each value grows by 16ms. i tried:
>  - manually set the cpu_scaling to a fixed frequency
>  - running two instances of burnMMX to keep both cores busy
>  - lowering the voltage step-by-step from the highest value and wait
> half a minute or so on each voltage
>
> i could go all the way down to 0 and there was still no crash. however,
> after stopping sometimes one and sometimes both instances of burnMMX, i
> got an immediate crash. i thought, that i might be testing the wrong
> frequency, since the fids list is a bit confusing - it looks like this:
> 13 12 10 8 6 136 - and it is not quite clear, which fid belongs to which
> frequency. because i was unsure about that, i wrote a script, that let
> me change the voltage of all frequencies simultanously. still, i
> experienced the same behaviour. 
>
> i ended up estimating good values and somehow i think it works, since at
> least in idling mode, the processor is cooler than it is without
> linux-phc enabled (49°C compared to 54°C). still, i think, it still
> could be optimized, but i couldn't figure a way to reliably find the
> optimal values.  
>
> probably someone on the list knows how to 'correctly' determine the good
> values for multi-core cpu in general or for the core 2 duo specifically.
>
> hm.. i just noticed, that the cpu from the x200s is a low-voltage cpu
> (SL9400). i wonder, if there is some room left for optimization on such
> model.s
>
>
> roman
>
>
>
> On Wed, 2009-03-11 at 15:54 +0100, Fabian Henze wrote:
>   
>> Am Mittwoch 11 März 2009 12:11:52 schrieb Volker Krueger:
>>     
>>> There, they reduce the power consumption by also fiddling with the CPU
>>> voltage, which sounds totally crazy...
>>> Can that seriously be done? What are the dangers?
>>> Who has done it?
>>>       
>> There is nothing crazy about that. As long as you just lower the voltage you 
>> can't damage the hardware. However if you lower it too much your system might 
>> (or will) crash.
>> Sadly linux-phc is not working on my Thinkpad R61 (Core2 T7300, I can set 
>> voltages to 0 0 0 0 and nothing happens, any ideas?), but I am using it on two 
>> Pentium M norebooks I have here and the results are impressive :)
>>     
>
>
>
> 		
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