The War of the SoCs: Performance/Watt

As we mentioned earlier, it is not that easy to determine the performance per watt of the different SoCs. Depending on the motherboard feature richness, performance per watt can vary a lot. We tested the Xeon E3-1240 v3 only on the feature-rich ASUS P9D, while the Atom C2750 is on a very efficient and simple HP m300 cartridge. Given the discrepancies, we cannot simply divide the performance by the power consumption and called it a day. No, we have to do a few calculations to get a good estimate of the performance/watt.

The current idle power of modern Intel CPUs is so low that it is almost irrelevant. All cores but one are put in a deep sleep (power gating), and the one that is still active runs at a very low clock and voltage. We have found that a Xeon E3-1200 v2's (Ivy Bridge) idle power is around 3W, perhaps even less... it is very hard and time consuming to measure correctly. We know from the mobile device reviews that the Haswell idle power is even lower. The Atom core is simpler, but the sleep states are slightly less advanced. Regardless, whether a CPU consumes 1.7W or 2.2W idling is not relevant for our calculation.

If we take the delta between idle power of a system and full load, and add about 3W idle, we're probably very close to the real power consumption of an Intel CPU. The only noise is the loss of the power supply (low because these are highly efficient ones) and the fact that the voltage regulators and DRAM consume a little more at higher load. Again, we are talking about very low numbers.

In the case of the Xeon E3, we also add about 3W for the Intel C224 chipset (0.7W idle, 4.1W TDP). For the X-Gene, we may assume that the idle power is a lot higher. When we calculated the power of the different components (8 DIMMs, disabled 10 GbE, etc.), we estimate that it is about 10W.

For the total system power, the power consumption of one node, we take the m300 numbers as measured. We subtract 7W from the m400 numbers as the m400 has four extra DIMM slots and a 10 GbE NIC. We add 9W to the SoC power of the Xeon E3 as we have found out that 12W is more or less the power that a Xeon E3 node consumes without the SoC.

Power Consumption Calculations
SoC Power Delta =
Power Web -
Idle (W)
Power SoC =
Power Delta +
Idle SoC +
Chipset (W)
Total System Power =
Power SoC +
Mobo (W)
Xeon E3- 1240 v3 3.4 95-42 = 53 53+3+3 = 59 53+3+12 = 68
Xeon E3-1230L v2 1.8 68-41 = 27
(45-18 = 27)
27+3+3 = 33 27+3+12 = 42
Xeon E3-1265L v2 2.5 65-26 = 39 39+3+3 = 45 39+3+12 = 54
Atom C2750 2.4 25-11 = 13 13+3+0 = 16 25
X-Gene 67-37 = 30 30+10 = 40 67-7 = 60

Let's discuss our findings. The Xeon E3-1240 v3 consumes probably about 50W with a high web load and is nowhere near its TDP (80W). The Xeon E3-1265L v2 (45W TDP) and Xeon E3-1230 (25W TDP) consume probably slightly more than their advertised TDP. That is slightly worrying as an integer workload that raises the CPU load to about 85-90% is not the worst situation you can imagine.... a 100% FPU load will go far beyond the TDP numbers then. The Atom C2750 requires the least power.

Performance per Watt
SoC Total Power
(SoC + Chipset)
at 1000ms
Throughput per
Watt (SoC)
Throughput per
Watt (System)
Xeon E3- 1240 v3 3.4 59 68 1221 20.7 18
Xeon E3-1230L v3 1.8 33 42 739 22.4 17.6
Xeon E3-1265L v2 2.5 45 54 759 16.9 14.1
Atom C2750 2.4 16 25 312 19.5 12.5
X-Gene 1 2.4 40 60 322 8 5.4

We are not pretending that our calculations are 100% accurate, but they should be close enough. At the end of the day, a couple Watts more or less is not going to change our conclusion that the Xeon E3-1230L v3 and Xeon E3-1240 v3 are the most efficient processors for these workloads. The Xeon E3-1230L v3 wins because it will require less cooling and less electricity distribution infrastructure using the same dense servers.

The Atom wins if you are power limited but the power efficiency is a bit lower when it comes to serving up a web infrastructure. Lastly, the X-Gene 1 has some catching up to do. The X-Gene 2 promises to be 50% more efficient. The software optimization efforts could bridge the rest of the gap, but we don't have a crystal ball.

Web infrastructure Power consumption Conclusion


View All Comments

  • gdansk - Monday, March 09, 2015 - link

    xgene is not looking so great. Even if it is 50% more efficient as they promise they'll still be behind Atom. Reply
  • Samus - Monday, March 09, 2015 - link

    HP Moonshot chassis are still *drool* Reply
  • Krysto - Monday, March 09, 2015 - link

    The main problem with the non-Intel systems is not only that they use older processes compared to Intel, but that they use older processes even compared to the rest of the non-Intel chip industry. AMD is typically always behind 1 process node among non-Intel chip makers. If they'd at least use the cutting edge processes as they become available from non-Intel processes, maybe they'd stand a chance, especially now that the gap in process technologies is shrinking. Reply
  • Samus - Monday, March 09, 2015 - link

    AMD simply isn't as bad as people continually make them out to be. Yes, they're "behind" Intel but it's all in the approach. We are talking about two engineering houses that share nothing in common but a cross licensing agreement. AMD has very competitive CPU's to Intel's i5's for nearly half the price, but yes, they use more power (at times 1/3 more.)

    But facts are facts: AMD is the second high-tech CPU manufacture in the world. Not Qualcomm, not Samsung. It's pretty obvious AMD engineering talent spreads more diversity than anyone other than Intel, and potentially superior to Intel on GPU design (although this has obviously been shifting over the years as Intel hires more "GPU talent.")

    AMD in servers is a hard pill to swallow though. If purchasing based on price alone, it can be a compelling alternative, but for rack space or low-energy computing?
  • Taneli - Tuesday, March 10, 2015 - link

    AMD doesn't even make it in top 10 semiconductor companies in sales. Qualcomm is three, Samsung semicondutors six and Intel almost ten times the size of AMD.

    Outside of the gaming consoles they are being completely overrun by competition.
  • owan - Tuesday, March 10, 2015 - link

    I'm sorry, at one point I was an AMD fanboy, back when they actually deserved it based on their products, but you just sound like an apologist. Facts are the facts, FX processors aren't competitive with i5's in performance or power or performance/$ because they get smacked so hard they can't be cheap enough to make up for it. Their CPU designs are woefully out of date, their APU's are bandwidth starved and use way too much power to be useful in the one place they'd be great (mobile), and their lagging process tech means theres not much better coming on the horizon. I don't want to see them go, but at the rate ARM is eating up general computing share, it won't be long before AMD becomes completely irrelevant. It will be Intel vs. ARM and AMD will be an afterthought. Reply
  • xenol - Wednesday, March 11, 2015 - link

    Qualcomm is used in pretty much used in most cell phones in the US to the point you'd think Qualcomm is the only SoC manufacturer. I'm pretty sure that's also how it looks in most of the other markets as Korea. Plus even if their SoCs aren't being used, they're modems are heavily used.

    If anything, Qualcomm is bigger than AMD. Or rather, Qualcomm is the Intel of the SoC market.
  • xenol - Wednesday, March 11, 2015 - link

    [Response to myself since I can't edit]
    Qualcomm's next major competitor is Apple. But that's about it.

    Also I meant to say other markets except Korea.
  • CajunArson - Monday, March 09, 2015 - link

    Bear in mind that the Atom parts were commercially available in 2013, so they are by no means brand-new technology and the 14nm Atom upgrades will definitely help power efficiency even if raw performance doesn't jump a whole lot.

    Anandtech is also a bit behind the curve because Intel is about to release Xeon-D (8 Broadwell cores and integrated I/O in a 45 watt TDP, or lower), which is designed for exactly this type of workload and is going to massively improve performance in the low-power envelope sphere:
  • SarahKerrigan - Monday, March 09, 2015 - link

    14nm server Atom isn't coming.

    "Atom will become a consumer only SoC."

Log in

Don't have an account? Sign up now