Interesting thought on Performance/Watt

lopri

Elite Member
Jul 27, 2002
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I ran into this short but intriguing idea while reading @Beyond3D and I thought I'd share it with my fellow AT'ers. It's a very sharp thinking, when 'Performance/Watt' seems to become the most important thing in tech scenes for the past couple of years. While I don't disagree that high performance and low power usage is a good thing, but it is always interesting to look deeper to see by who, when, for what this new 'discourse' is being driven.

If you want low power consumption, buy a laptop or an old DX5 GPU. Higher performance (for irreversible computations) inevitably requires more power (Landauer's principle). Simply plot the performance vs power requirements for either CPUs or GPUs over the last number of years. So if you want faster and faster GPUs, you need to get comfortable with continually higher power requirements.

The push by chip vendors to make chips more power efficient is simply an economic concern from their part. When power consumption was relatively low compared to other equipment or parts of the system, costs were mainly silicon driven. Now that performance has scaled to the level that the costs of acceptably quiet cooling solutions are becoming a significant part of overall delivery costs, then making chips more power efficient becomes more of a priority, with a tradeoff between more complex silicon design and more die area given toward power efficiency.

When chips were silicon constrained, the priority was given to minimizing die area and maximizing freqency to maximize the performance/die area ratio and thus maximize the performance/cost ratio. As chips become power constained, you maximize the performance/cost ratio by maximizing the performance/power ratio instead. This leads to the rather interesting reversal of emphasis, since increasing the power efficency means reducing the frequency and increasing the die area (more transisters running at lower frequencies). This is because power scales up nonlinearly with frequency but performance only scales linearly with frequency. However, both power and performance scale linearly with transistor count. As a result, in the future you will see more and more chips primarily increase performance by dramatically increasing transitor count rather than frequency.

From a buyers point of view, the main differences are total cost of the equipment as well (the cost of the power differences are small). The other considerations (noise, etc.) all have solutions that simply add to the cost.

So if you had two machines available that had the same quietness, the same features, the same reliability and the same performance, etc. but one was 25% less expensive, most would choose the less expensive one. 12 months later, if they took their machine apart, examined it with a volt meter and noticed a sophisticated heat exchanger mounted on the chip, and realized that it had a higher power consumption than the other machine that they didn't buy, would they care much?

The original thread can be found here: http://www.beyond3d.com/forum/showthread.php?t=39363
 

KingstonU

Golden Member
Dec 26, 2006
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I want my GPU to have the same or less TDP then my CPU!!

Is it not ridiculous when the graphics use 180W and the best CPU uses 125W max! and can come in as low as 35W or 65W?
 

firewolfsm

Golden Member
Oct 16, 2005
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I don't agree with that, as transistor size gets smaller there's no reason we can't improve power consumption while still improving performance, on top of that, there's no reason a more efficient architecture can't improve power AND performance, Core2 over Netburst is a perfect example of this.
 

91TTZ

Lifer
Jan 31, 2005
14,374
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Originally posted by: firewolfsm
I don't agree with that, as transistor size gets smaller there's no reason we can't improve power consumption while still improving performance, on top of that, there's no reason a more efficient architecture can't improve power AND performance, Core2 over Netburst is a perfect example of this.

I agree. That article was bunk.
 

Goi

Diamond Member
Oct 10, 1999
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Actually power scales linearly with frequency. 1/2(CV^2)(activity)(freq) IIRC.
 

firewolfsm

Golden Member
Oct 16, 2005
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Originally posted by: Goi
Actually power scales linearly with frequency. 1/2(CV^2)(activity)(freq) IIRC.

Until you start raising the voltage to accomadate for the high frequency.
 

zephyrprime

Diamond Member
Feb 18, 2001
7,512
2
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I agree with the article. "performance/watt" has become a marketing mantra just like megahertz was before. Higher computational speed necessitates higher power because of the laws of physics. Improving design and technology can ameliorate this fact a lot but cannot obviate it.