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What is the function that describes the relation between CPU utilization and consumption of energy (electricity/heat wise).

I wonder if it's linear/sub-linear/exp etc..

I am writing a program that decreases the CPU utilization/load of other programs and my main concern is how much do I benefit energy wise..

Moreover, my server is mostly being used as a web-server or DB in a data-center (headless).

In case the data center need more power for cooling I need to consider that as well.. I also need to know what is the effect of CPU utilization on the entire machine power consumption ..

DuduAlul
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    Modern CPUs + OSs can up/down clock the CPU to meet demand. The CPU will operate at the lowest clock speed necessary to cope with the load on it. Consider these in-built features before writing your own program. – Jon Cram May 25 '11 at 18:34
  • thanks for your comment, I am trying to reduce the load. – DuduAlul May 25 '11 at 18:40

2 Answers2

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Here you can find a short ppt answering your questions, and providing additional info.

Although there is no Copyright notice in the ppt, the work is probably protected, so I will copy here only three graphs relevant to your main question and follow-ups in comments.

enter image description here

enter image description here

enter image description here

HTH!

Community
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Dr. belisarius
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For the CPU alone linear would be the most likely.
It gets complicated with CPUs that can reduce the clock speed under low load (like laptops) but for a server it's probably a good approximation.
Remember though that the CPU isn't the only component - you have to multiply by the percentage of power the CPU is using compared to the entire system.

Martin Beckett
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  • Adding onto Martin's answer, another factor is the hard drives in use. Generally commercial grades drives keep constant velocity 24/7 until they break, but some drives will slow down or completely halt after a certain point of being idle. Coming out of standby will spike load temporarily as the drive motors exerts higher then normal force. This can happen randomly based on the needs of the server's running applications and caches. – David May 25 '11 at 18:37
  • thanks, what is the avg percentage of power the CPU is using comparing to the entire system? – DuduAlul May 25 '11 at 18:37
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    Depends what else is in the system! A Xeon can burn 85W but so can a top end graphics card. Best way is to get a wall power meter (kill-a-watt) and try it. – Martin Beckett May 25 '11 at 18:44
  • if we are talking about a web server in a data center, can we assume that the CPU utilizes most of the electricity? – DuduAlul May 25 '11 at 18:50
  • A headless server with no disks then the CPU is probably more than 50% of the power consumption - yes – Martin Beckett May 25 '11 at 19:22