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Sandy Bridge-E’s Efficiency Suffers Significantly Overclocked

Overclocking: Can Sandy Bridge-E Be Made More Efficient?
By , Achim Roos

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.

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Top Comments
  • 20 Hide
    Yargnit , February 17, 2012 4:00 AM
    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?
Other Comments
  • 2 Hide
    mayankleoboy1 , February 17, 2012 3:45 AM
    This article appeared on tomshardware.de weeks before.
  • 0 Hide
    Combat Wombat , February 17, 2012 3:55 AM
    Good to know!
  • 20 Hide
    Yargnit , February 17, 2012 4:00 AM
    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?
  • 0 Hide
    billj214 , February 17, 2012 4:08 AM
    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!
  • 6 Hide
    Marcus52 , February 17, 2012 4:08 AM
    Quote:
    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.

    ;) 
  • 2 Hide
    Marcus52 , February 17, 2012 4:34 AM
    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.

    ;) 
  • -3 Hide
    lahawzel , February 17, 2012 4:40 AM
    "Intel Core i7-3690X Extreme Edition"

    Tom's Parallel Universe Hardware.
  • 1 Hide
    giovanni86 , February 17, 2012 4:52 AM
    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
  • -7 Hide
    Naxos , February 17, 2012 5:11 AM
    Does anyone spending 600-1k$ on a cpu really care about efficiency??
  • 2 Hide
    cangelini , February 17, 2012 5:34 AM
    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. =)
  • 1 Hide
    cangelini , February 17, 2012 5:34 AM
    mayankleoboy1This article appeared on tomshardware.de weeks before.

    Which makes sense since it was written in German =)
  • 0 Hide
    Reynod , February 17, 2012 10:17 AM
    http://www.youtube.com/watch?v=lrN1jm9aLq0

    /raises beer stein ...

    :) 
  • -1 Hide
    visz963 , February 17, 2012 11:01 AM
    What a big surprise
  • 5 Hide
    stingstang , February 17, 2012 12:48 PM
    gsxrmemy 2600k @ 5.1GHz 1.5v (49/103) will eat this CPU for lunch when playing games. Thx to Gskills 2200Mhz cas7 ram.

    So are all....SOOO impressed by your dangerously overclocked processor. Thank you so much for making that comment.

    In other news...
    Maybe you guys should have gone backwards a little to see if underclocking would increase the efficiency by a greater factor than the performance loss?
  • -6 Hide
    nss000 , February 17, 2012 12:50 PM
    Oh Nooooooooo! All we need is a decent webzine pimp (overclocking) krak to the byteboyz (occaine addicts)! It's a waste of **MY** resources when a company "cheats down" its nominal specs , catering to a lost ranting, kanting tribe of light-shunning, babble-voiced 11-yo gamerz, gonzos and gnuguruz .. all pretty much talking and acting like ... well .. you know who!

    If they all took a bath in liquid Nitrogen then **decent-minded** casual lusr userland would be well-served with the fastest-possible **default** system performance.

    Don't feed the animals, Tommy-me-laddie.....
  • 0 Hide
    jaquith , February 17, 2012 2:33 PM
    Very nice article! Thanks for the efficiency data - food for thought :) 

    I would agree though be it a somewhat modified multiplier approach, at least for 'my' environment and dependent on 'how' your applications are threaded using 45x/44x/43x. Currently, I'm playing with x48/x47/x46 and Strap values; If you have an ASUS MOBO -- here's a good OC'ing guide -> (scrub to 16 min) http://www.youtube.com/watch?v=Kx2z07sFM2I Again, it all depends on your: 1. vCore (luck of the CPU draw), 2. Thermal (temps/cooling), 3. Applications used.

    In addition, I really recommend using 'BIOS Profiles'; example if during the day I'm not doing anything stressful then I'll use a 'Stock' profile, or 'Gaming' profile, or 'Rendering' profile. Each tailored to the environment, a simple BIOS load and reboot you've got what you need from the SB-E.

    'My' selection for a limiting factor is the vCore and in essence the heat, I really don't recommend a vCore >1.45v -- so that's my limit. Every SB-E will offer, luck again, different stability per a designated vCore. I also have seen enough data to know both MOBO and Cooling aide signification enough.
  • 0 Hide
    Anonymous , February 17, 2012 2:41 PM
    What cooler was used?
  • 0 Hide
    bin1127 , February 18, 2012 5:46 AM
    I like how it shows a minor increase in power use allows for a big gain in productivity; and then it tapers off.

    Do motherboards allow overclock profiles in the bios so you don't have to manually input new figures to 'turn on/off' overclocking?
  • -3 Hide
    triny , February 18, 2012 2:01 PM
    The 2500k is top dog
    6 cores? no one needs them
    over 1000$ ? craziness
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