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The truth about CPU power consumption

Discussion in 'Processors and Motherboards' started by sub.mesa, Dec 30, 2010.

  1. sub.mesa

    sub.mesa New Member

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    Power consumption can be an interesting topic when you're building a home server system that runs 24/7. To estimate the maximum power consumption of your CPU you can look at the Thermal Design Power or TDP values that are provided by the CPU manufacturer. Common values include 45W, 65W and 95W.

    TDP not a magic bullet
    However, TDP itself won't tell you how much power the chip consumes; it's a thermal specification to describe what amount of heat the casing/environment would need to be able to dissipate, in order for it not to overheat (stay below Tmax value).

    Also, TDP does not even accurately predict maximum power consumption; three chips clocked slightly different of eachother but belonging to the same family might all three share the same TDP, but still the higher clocked version will consume more power when fully stressed.

    Idle power consumption is what you should look for!
    Instead of looking for TDP or maximum power consumption, for a 24/7 server what you actually want is a very low idle power consumption. Idle means when you're not really doing anything, which is where all the modern power saving technologies come into play!

    Advanced power saving
    Modern CPUs of both AMD / Intel are very low idle power. Intel has the best manufacturing process, able to sell 32nm High-K Metal Gate CPUs that have very low leakage and thus low idle power consumption, even when turning some power saving techniques completely off. AMD relies heavily on its Cool'N'Quiet technique, which both throttles clock frequency and voltage, but is very successful at reducing idle power consumption as well; as long as this power saving technique is activated in both BIOS and Operating System.

    What to look for?
    The result of all this power saving is that a six-core AMD chip uses less idle power consumption than an older AMD Sempron, with much less sophisticated power saving and older production process. Most modern CPUs of both AMD (45nm) and Intel (32nm) would be a good choice. The AMD Phenom with its higher caches would consume a bit more than the Athlons, but it's not much. Any modern CPU should be <10W at idle.

    Platform power
    With CPU power kept at a low, the platform power is up next. This includes the motherboard, memory, chipset, graphics, network, controllers, etc. The more modern platform generally the lower/better the idle power consumption.

    An interesting note here is the earlier Atom platforms, where the CPU consumed only a couple watts, while the chipset did more than 10 times that amount, so these platforms actually consume more idle power than recent AMD six-core systems are capable of! Same story for Intel 32nm and efficient chipsets; though Intel platform has more power consuming chipsets at the moment.

    What's up next?
    In the not-too-distant horizon we can see interesting storage platforms based on AMD Zacate platform (the AMD competition to Intel Atom) and Intel Sandy Bridge architecture, which adds significant performance gains and like AMD Fusion, combines CPU and GPU in one die/package.

    If you're looking for a low idle power system, the AMD Zacate platform should be very interesting to you. Platform power is as low as 9 Watts as measured on a beta-board thus far. This sounds very promising and would both pack reasonable performance, high performance I/O with very low idle power. You would be able to get a 1.2GHz dualcore or 1.6GHz dualcore with gigabit ethernet, PCI-express 2.0 x16 and 6x SATA/6Gbps at your disposal; all this for a few watts? It almost sounds unbelievable!


    Feel free to share your thoughts. :)
     
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  2. Patrick

    Patrick Administrator
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    One very important note to the above is that fans actually consume a ton of power. The Norco RPC-4220, for example, has six fans in its stock configuration. Four of those six stock fans reside in the middle partition and are rated at 4.2w each for a total of 16.8w from just those four fans that will go constantly as long as the server is on. With today's low-power CPU's and platforms, fans can actually consume 30w+, or more than many CPU-motherboard-RAM configurations do at idle.

    Also, an important note on CPU TDP is that the TDP values are for the package. For example, a Core i3-550 may have a 73w TDP, and an Athlon II may have a 65w TDP, but one has to remember that the Core i3 architecture includes an on die north bridge and GPU. On an AMD platform one needs to look at both the TDP of the CPU and north bridge to come up with an equivalent figure to the Core i3 package. This is a primary reason the new Atom D510 uses much less power than the Atom N330 + Intel 945 chipset, and that the Atom N330 had lower platform power consumption with the NVIDIA ION north bridge/ GPU.

    One should also note that installing a system with onboard GPU (for example for an IPMI 2.0 KVM-over-IP implementation) the CPU with an onboard GPU will have to factor in the additional server chipset power draw.
     
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  3. OBasel

    OBasel Active Member

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    are you sure about 4.2w each at full speed? that means that server cases will use a lot of power for fans.
     
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  4. agnes james

    agnes james New Member

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    Monitor - 100 watt
    CPU - 60 watt
    Total = 160 watt

    If u keep it on for 1 hours it will consume 0.16 units

    & on other hand its dependent on your usage.. & now there are many steps like:-

    1. Buy a voltmeter
    2. Use a laptop instead of a desktop. Or a tablet or smartphone.
    3. Use a flat panel display instead of a CRT monitor
    4. Buy Energy Star equipment etc. etc.
     
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  5. Lost-Benji

    Lost-Benji Member

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    There is another factor being missed, PSU efficiencies and Power Factor. Most supplies these days are getting very good at being efficient (less energy wasted as heat/noise) and then there are those that can present the mains feed with very close to 1:1 PF.
    I am not going to get into the full topic of PF as I already understand it just fine, if you are not sure what it is, Google it. The end result of a poor PF value is that you will be paying more money on your power bills than you need to.


    Pat mentioned fan draw, yes, there are fans that will suck up small kids at ten paces with ease and they draw enough power to dwarf a GM 6/71 blower.
    I have some fans sitting in a old SC5300 Intel chassis that draw just under 4.4A a piece @ 12V, yes kiddies, that is a 50W case fan, not bad for 120mm. Oh, and there is two of them in series then add the 100mm pair just below them.
    The case makes a Boeing 747-400 blush.
     
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  6. PigLover

    PigLover Moderator

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    Those fans in the Norco's are nothing. The stock fans I pulled from my C6100 are rates at 4.9 amps @ 12v (yes, 4.9 AMPS, not watts). Means at full speed they can draw just shy of 60 watts each. With four of them in the chassis you could see well over 200 watts drawn just by the fans.

    Good news is that they don't run full speed very often and power-draw is non-linear to RPM, so at "normal" operating speeds they draw much, much less.

    So yes, in server cases - especially better ones like the ones from SuperMicro and Chenbro or "repurposed" HPs/Dells - the fans do contribute significantly to the power draw.
     
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  7. uberguru

    uberguru Member

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    Does anyone know the full load power from the Intel Xeon E5-2660 CPU? Yes it has TDP of 95W but is it accurate to think it should max out at 75W? 85W?
     
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  8. Biren78

    Biren78 Active Member

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    Sorry gotta ask - what type of "full load"? Full load for a web server is probably a few watts less than a synthetic benchmark like prime95 or super pi. TDP is rated for those extremes.
     
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  9. uberguru

    uberguru Member

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    for a web/database/app server
     
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  10. Boddy

    Boddy Active Member

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    Interesting article on PSU efficiency: http://www.tomshardware.com/reviews/power-supply-protection-calculate-consumption,3066-2.html
     
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  11. mackle

    mackle Member

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    Idle/full load power consumption also leads to important considerations for those considering compute nodes, especially those that may be able to run non-24/7.

    An environment that allows for the easy firing up of a compute node to undertake on-demand tasks (rendering/CAD/transcoding/etc) or scheduled tasks (archiving/database operations/etc) potentially leads to significant power savings, if it can be incorporated. It also reduces the importance idle consumption, except perhaps in deciding whether it is worthwhile to run 24/7 or on-demand.

    Alternatively of course, for nodes that compute 24/7 - one that allocates spare resources to Folding@home for example - idle consumption is effectively irrelevant unless you're interested in how much electricity you're consuming for the 'cause'. :)
     
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  12. spyrule

    spyrule Active Member

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    2010 to 2014 in only 11 posts... This conversation is positively glacial!
     
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  13. Boddy

    Boddy Active Member

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    In the age of global warming and melting of glacial ice caps, the subject of power consumption is very pertinent! :D:p;):rolleyes:
     
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  14. spyrule

    spyrule Active Member

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    Shouldn't that be sunscreen and swimming lessons?
     
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  15. NeverDie

    NeverDie Active Member

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    Agreed. So why is it so hard to find out what it is? TDP is easy to find on ARK. But where do I look to find idle power?

    I wish there was an idle power calculator, where you could specify the CPU, the motherboard, the RAM, etc., and it would provide the total as well as the idle power for each component.
     
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  16. Patrick

    Patrick Administrator
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    Idle power can vary a lot TBH. Drives make a huge difference. Power supply, BIOS settings, network cable lengths. And then more practically, the real world idle can be different than testing. Real world there are usually some processes working at a given time. When idle is 200w many of these things are rounding errors. When idle is 8-40w they start having a bigger impact.
     
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  17. T_Minus

    T_Minus Moderator

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    Idle power of the CPU i've seen in some intel docs, they will break it down by which power state it goes to as well.
    I also recall seeing on some motherboards the option to set the LOWEST frequency the CPU would drop to in xState ... I haven't seen this before or used it but thought it was cool.
     
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  18. Patriot

    Patriot Moderator

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    Unfortunately while there are registers to tell what C-state and P-state you are in there are no registers to tell what T-state you are in.
    So turbo throws a wrench into any calculations you may be doing. Power meter and day averages are by far the easiest approach.
     
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  19. HellDiverUK

    HellDiverUK Active Member

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    With the same i3-4350, I've seen idle consumption anywhere between 22W and 48W. That's with different boards, different PSUs, but the same single SSD (Intel Pro SSD 1500 180GB) and RAM (2x2GB Samsung DDR3L-1600). Single Intel retail cooler.

    The lowest consumption was on an MSI B85M-Eco, the worst an AsRock E3C226D2I. The best PSU is a 150W FSP 1U unit, next best is probably a Corsair CS450M.

    The second lowest idle consumption is probably the Lenovo TS140 with the i3 fitted, using the stock Lenovo fans and the stock 450W 80Plus Platinum PSU. It idles around 26W. The Lenovo's odd PSU plug means I can't easily test that supply with the other boards.

    For truly terrible idle consumption, it has to be my AMD FX8320E on an Asus 760G board. It rarely sees below 60W, and can peak over 180W when all 8 cores are loaded. It is a very, very good ESXI host, though.
     
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  20. T_Minus

    T_Minus Moderator

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    I would imagine the PSU variance would be do to the "Sweet spot" of utilization based on their rating. IE: The 150w is REALLY efficient where the 500W you're not in the efficiency utilization 'range' so there's a decent % wasted unfortunately. I recall see graphs someplace for this for each PSU.
    Another thing to keep in mind is that I believe haswell requires one of the 'new' power supplies to use the lowest power state. (Someone back me up on this as i'm not 100%)
     
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