Overclocking: Can Sandy Bridge-E Be Made More Efficient?

Features
By Achim Roos, Patrick Schmid
published

Intel's six-core processors are fast, but enthusiasts almost always want to push unlocked multipliers harder. Core i7-3960X can easily exceed 4 GHz, but what happens to power efficiency when clock rates go up? Sandy Bridge-E demonstrates weaknesses there.

Sandy Bridge-E’s Efficiency Suffers Significantly Overclocked

The results speak for themselves. While Intel’s Core i7-3960X is certainly the fastest processor money can buy, and although it offers plenty of overclocking headroom, its efficiency suffers tremendously when you push it beyond its stock specifications. Given its complexity and target market, there's simply no way for the LGA 2011-based chips to compete against the fast, yet relatively lower-power LGA 1155-based models like Core i5-2500K and -i7-2600K.

Is that a problem? For the folks who need the performance of an LGA 2011-based configuration, probably not. The Sandy Bridge-E die incorporates a four-channel memory controller, 40 lanes of third-gen PCI Express, tons of last-level cache, and as many as six enabled cores. Despite the mature 32 nm process on which it's manufactured, it still takes a lot of power to drive such a complex SoC. 

Because power consumption is affected by both frequency and voltage, even turning up the clock rate without manipulating voltage impacts efficiency. The effect isn't pronounced under 4.5 GHz. However, each step of the way, efficiency does drop, as power use goes up faster than performance. Things get worse once voltage needs to be added, and our index tanks even faster. 

So, you can get a decent efficiency boost from Sandy Bridge's four cores through overclocking, but the same can't be said for Sandy Bridge-E. If you're tuning for absolute performance, rather than getting more done per watt of power use, we'd recommend using a 42x Turbo Boost multiplier for five/six active cores, a 43x multiplier for three/four active cores, and a 45x ratio for one or two active cores because this shows a significant performance improvement with reasonable increases in power consumption.

In the meantime, we'll eager await Intel's upcoming 22 nm-based Ivy Bridge chips, which promise to improve efficiency even further.

Achim Roos
Achim Roos
28 Comments Comment from the forums
  • mayankleoboy1
    This article appeared on tomshardware.de weeks before.
    Reply
  • Combat Wombat
    Good to know!
    Reply
  • Yargnit
    What about trying to under-volt it at slight under-clocks to slight-overclocks. How much room is there to reduce it's stock voltage to gain better efficiency?
    Reply
  • billj214
    Was there an efficiency chart made for the Core i7 2600k or 2700k?
    Nice to know Intel doesn't just set the stock clock speed for just performance!
    Reply
  • Marcus52
    And then there's the Core i7-3820, which only sports four cores, but operates at a base clock rate of 3.6 GHz. Although this less-complex chip could probably hit higher Turbo Boost frequencies, Intel limits it to 3.9 GHz to keep it from outshining the top-end Core i7-3960X in single-threaded tasks.

    Did someone at Intel tell you that was the reason for a lower Turbo Boost limit, or did you just assume it?

    I think we should be careful of this kind of guess at another person's, or company's, reasoning. There could be some other cause for the limit - for example, they will obviously sell it for a lower price, so wouldn't a possible reason be they have looser binning specs to allow for chips that wouldn't make it under more strenuous tests through? (Remember, Intel, or any CPU manufacturer, doesn't warrant the product based on what it can be pushed to, and is generally going to provide it at a clock rate they feel is safe over time to guarantee.)

    I'm certainly not saying it is a bad assumption, what you said makes sense to me, but I do think there are enough other reasonable possibilities that I wouldn't have stated it as a fact unless I knew it to be.

    ;)
    Reply
  • Marcus52
    Thanks for the analysis!

    I do think articles like this are very important; those of us who overclock, especially when we turn off all the power-saving features in hopes of reaching that max stable a CPU can do, should be aware of how much money we are spending if we keep said OC. It's more than just the high end cooling solution.

    The people that bash higher capacity PSUs could also stand to learn a thing or two, here. An overclocked CPU can require a huge amount of peak power over and above what a stock CPU needs (349W measured here). An overclocked Sandy Bridge-E and an overclocked GTX 580 could require a peak power of 650W just considering those 2 components!

    A Kill A Watt or similar device is a great way to measure how much you actually spend a month operating your computer. You might be surprised.

    ;)
    Reply
  • lahawzel
    "Intel Core i7-3690X Extreme Edition"

    Tom's Parallel Universe Hardware.
    Reply
  • giovanni86
    Just a thought, so at 4.7Ghz the performance increase was only 16%? For being such a High overclock i was hoping for more then that. You guys literally upped the bar from stock clock to the OC clock by 1.4ghz, seems like a small increase in performance if you look at the amount of watts it takes.. Well at least its good 2 know my future billing of electricity will sure be expensive.. =P
    Reply
  • Naxos
    Does anyone spending 600-1k$ on a cpu really care about efficiency??
    Reply
  • cangelini
    Marcus52Did someone at Intel tell you that was the reason for a lower Turbo Boost limit, or did you just assume it?I think we should be careful of this kind of guess at another person's, or company's, reasoning. There could be some other cause for the limit - for example, they will obviously sell it for a lower price, so wouldn't a possible reason be they have looser binning specs to allow for chips that wouldn't make it under more strenuous tests through? (Remember, Intel, or any CPU manufacturer, doesn't warrant the product based on what it can be pushed to, and is generally going to provide it at a clock rate they feel is safe over time to guarantee.)I'm certainly not saying it is a bad assumption, what you said makes sense to me, but I do think there are enough other reasonable possibilities that I wouldn't have stated it as a fact unless I knew it to be.Hence the "probably." Of course, we don't know for sure, nor would Intel ever admit as such, but it's an educated guess nonetheless. =)
    Reply