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Intel Core i7 4790K Energy Efficiency

Introduction

During the time of the first generation Intel Core i series, Tom's Hardware made an article about finding the most efficient clock speed for Core i5 750 http://www.tomshardware.com/reviews/core-i5-750-efficiency,2500.html and Core i7 920 http://www.tomshardware.com/reviews/overclock-core-i7,2268.html. I got curious as to what is the most efficient clock speed for my Core i7 4790K.



Test System

[CPU] Intel Core i7 4790K
[GPU] Gigabyte GTX 970 mini-ITX
[MOB] Gigabyte Z97-D3H (F7 bios)
[RAM] G. Skill Trident X 4GBx2 DDR3 @ 2400 MHz 10-12-12-31 2T
[HSF] Noctua NH-U12S

Windows 7 64-bit with Service Pack 1
GeForce 355.82



Test Methodology

For productivity testing, I only used HandBrake. The short movie (about 10 minutes long) Big Buck Bunny was encoded from AVI to MP4 using High Profile preset. Video resolution is 1080p. Big Buck Bunny is an open movie which was created using open software. You can download the movie here https://peach.blender.org/about/. To save time, I only encoded the first 60 seconds of the movie.

To know the energy used for encoding the video, I measured the time it took to complete the task then multiplied it by the power draw during the task. The clock speed and voltage with the lowest energy used will be the most efficient.

Turbo Boost was disabled.



Performance Results

The results below are the average of 3 runs

jUpbTNR.png



Conclusion

Overclocking Haswell reduces energy efficiency. Because every chip will differ in the required voltage for a given clock speed, it's hard to give a fixed value for the most efficient clock speed for Core i7 4790K. But based on my test, the most efficient clock speed for Core i7 4790K is the one that you can achieve with a core voltage of ~0.900 V.

Comments (3)

Thanks for the effort. I think energy efficiency should be looked at whilst also comparing how fast / better a given task is performed. For example, at 4000mhz, it's a 4.44% reduction in rendering time sequential & 8.51% decrease from stock, whilst power consumption went up 8.8% sequential and 21.43% from stock. Based on that, the absolute break even for performance : consumption would be at 4000mhz.
Efficient based on watts per OC is an interesting metric.

Is Handbrake CPU or GPU limited ? I like the simplified watt-second measurements.

Thanks for the information
Aww now I have to down clock my profile for daily computing/watching movies... 3.6 with this chip is still overkill for that using 2/3rds the energy. Would I even notice the slowdown? I doubt it. Maybe a few extra seconds from boot to desktop, maybe not...
Overclock.net › Articles › Intel Core I7 4790k Energy Efficiency