Processor Scaling

Ray Parrish crp at cmc.net
Wed Jan 7 00:50:07 GMT 2009


Michael wrote:
> Ray Parrish wrote:
>> Derek Broughton wrote:
>>   
>>> Ray Parrish wrote:
>>>
>>>   
>>>     
>>>> Well, as I said above I'm not worried about the extra power the "cpu"
>>>> not the whole desktop takes... The cpu is just a small chip inside the
>>>> box, and runs on 5 volts. Reading comprehension my friend...
>>>>     
>>>>       
>>> Electricity comprehension my friend.  5V or 500V is (largely) irrelevant - 
>>> it's the power, not the voltage.
>>>
>>>
>>>   
>>>     
>> Ok, I did some research, and this supports my view [From Wikipedia]
>>
>>   
>>> Dynamic frequency scaling reduces the number of instructions a 
>>> processor can issue in a given amount of time, thus reducing 
>>> performance. Hence, it is generally used when the workload is not 
>>> CPU-bound.
>>>
>>> Dynamic frequency scaling by itself is rarely worthwhile as a way to 
>>> conserve switching power. Saving the most power requires dynamic 
>>> voltage scaling too, because of the V^2 component and the fact that 
>>> modern CPUs are strongly optimized for low power idle states. In most 
>>> constant-voltage cases it is more efficient to run briefly at peak 
>>> speed and stay in a deep idle state for longer (called "race to 
>>> idle"), than it is to run at a reduced clock rate for a long time and 
>>> only stay briefly in a light idle state. However, reducing voltage 
>>> along with clock rate can change those tradeoffs.
>>>
>>>     
>> Article url below -
>>
>> <http://en.wikipedia.org/wiki/Dynamic_frequency_scaling>
>>
>> However, it uses more power than I thought as shown in the following quote -
>>
>> "Sempron 3400+ has a die size of 84mm^2 , produced on AMD's 90-nanometer 
>> silicon-on-insulator (SOI) process. It runs at 2.0GHz and features a 
>> 256KB L2 cache, and its max thermal power is 62 watts. "
>>
>>  From the following page -
>>
>> <http://www.extremetech.com/article2/0,2845,1841866,00.asp>
>>
>> So, although I'm not really using more power by setting my cpu scaling 
>> to Performance, it still uses more power than I thought.
>>
>> Later, Ray Parrish
>>
>>   
> >From another viewpoint:  My situation requires my computer to be 
> inside an enclosed space without a great deal of ventilation.  With 
> scaling my cpu runs at 1.3 ghz and about 48 degrees C and the gpu is 
> 58.  At full speed the temperature of the cpu raises to about 58 
> degrees.  If I go to windows and play something like Crysis or Fallout 
> 3 I have to keep the cabinet door open to prevent the computer from 
> crashing.  I can't check the speed or temp very easily but when I 
> reboot to Ubuntu the cpu is running over 60 degrees and the gpu is 
> over 65 degrees.  Also everything is running from batteries so power 
> matters to me. 
>
>
That's pretty hot! I converted your celsius numbers to fahrenheit, and 
48 C is 118 F. My computer purrs along at 104 F, and during a four hour 
virus scan of my Windows install, with the cpu maxed out the whole time, 
it never got over 107 F...

I very seldom play games, so I don't know how it would perform under 
those conditions.

Later, Ray Parrish--

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