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Old 2008-08-24, 00:16   #1
biwema
 
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Mar 2004

3·127 Posts
Default Energy saving with AI Nap mode

I played around with the functions of my new mainboard and noticed that the AI Nap mode can be used for number crunching. At the beginning I thought that such an energy saving mode will also reduce the speed of the processor, but that is not the case. All cores run at full speed. It is even possible to continue downloads or record from the TV card.
The main difference is that it shuts down devices which are not used and reduces the core voltage of the CPU. During that time, there is no speaker and VGA output. (So it could be that some skype calls are missed). I noticed that there is no energy saving function on my (passive cooled) graphic card. It can turn off the signal, but the GPU does not get colder.

The following measurements I performed with Prime95 (1-4 Instances and a 2560k FFT Candidate)
Primary power of computer; Core Voltage of CPU; Iteration time

Normal mode:
Idle system: 89.8W 1.232 V
1 Instance: 118.4 W 1.192 V (57.6ms)
2 Instances: 137.9 W 1.168 V (60.1ms)
3 Instances: 146.6 W 1.160 V (67.1ms)
4 Instances: 152.0 W 1.160 V (77.2ms)

AI Nap mode:
Idle system: 87.7W 1.128 V
1 Instance: 111.4 W 1.096 V
2 Instances: 128.8 W 1.080 V
3 Instances: 136.0 W 1.072 V
4 Instances: 141.0 W 1.064 V

Torture Test on all cores:
Normal mode: 153.3 W; 1.160 V - AI Nap mode 141.2 W; 1.064 V

The iteration time gets higher when running more instances due to the memory bottleneck.
When running 4 instances of LLR with 1.6 million bit candidates I get 144.5 W (normal mode) 131.2 W (AI Nap). At that size there is almost no impact on the iteration time when running more than one instance.
When I saw that the Core voltage is reduced, I was not sure, how reliable the results will be. That’s why I ran the torture test for some time without any errors.

AI Nap mode can reduce the use of electricity by up to 10% and even keep the CPU cooler and the fan quieter.

Are there any other experiences or problems with the AI Nap mode? Do you also use it when not working at the computer? I wonder why I don’t find much about it in the internet.
I am not sure but i assume that AI Nap mode is only available on Asus mainboards and I don't know either which mainboard support it.


Hardware:
Mainboard: Asus P5KC; Memory 2 * 1GByte DDR2 PC5300; 667MHz CL5
CPU: Intel core2Quad Q9450 45nm, 2.66GHz, 12M L2, 1333MHz
CPU Cooler: Freezer 7 Pro with heatpipes; (fan can keep CPU below 55C with less then 1000 rpm while running Prime95 torture test on all 4 cores)
Power supply: >80% efficiency, Power factor >0.98

Background:
I had an Intel P4 3.4 GHz with an Asus P5LD2 Mainboard. One day the computer shut down and it was not possible anymore to restart it. After some research it turned out that there was a shortcut on the mainboard. I decided just to buy a new Mainboard and Processor and kept the memory and drives. It was even not necessary to reinstall the system or reactivate Windows.
That is the reason why I am running slow DDR2 modules I already used before.
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