Energy consumption and efficiency
In our previous articles on processors, we measured energy consumption in load in Prime95. This stress test has the merit of pushing the various architectures to the limit in a pretty equitable manner, but we weren’t able to use it to compare energy consumption and performance as the Prime95 benchmark consumes less and isn’t as balanced between processors.
We therefore decided to look for another application that would give us a level of performance and energy consumption representative of what we obtained on the other applications in our test protocol. In the end we opted for Fritz Chess Benchmark once again. In addition this application has the advantage of allowing us to fix the number of threads to be used easily.
The energy consumption readings therefore shouldn't be taken as absolute maximum values but rather as typical of a heavy load - applications specialised in processor stress such as Prime95 can consume up to 20% more. All energy economy features, including those on motherboards such as the ASUS EPU, were turned on for this test, as long as they didn't have a negative impact on performance:
[ 220V wall socket ] [ ATX12V ]Having got rid of the X58 Express chipset, the LGA 2011 platform is much more economical at idle than LGA 1366, without however performing at the same level as LGA 1155. In low load (1 thread) we’re down on LGA 1366 but we’re not far off. The same goes for maximum load (12 threads). Note that in load, energy consumption at the socket increases by 5 Watts when you go from 2x4 GB to 4x4 GB, which has an impact on the LGA 1366 and 2011 platforms which are equipped with three or four bars compared to two bars for the others.
The reading at the ATX12V allows us to isolate processor consumption. Unfortunately however, the figures are not entirely comparable as in certain cases some of the CPU consumption comes from the standard ATX 24 pin socket. To get a totally accurate comparison however, we can compare processors using the same motherboard. Note that the Core i7-3960X is the Intel CPU that draws most at the ATX12V in load.
We then looked at the energy efficiences of the different processors. To get a representation of this you have to divide the performance levels obtained in Fritz Chess Benchmark by CPU energy consumption. The only problem is however that it’s impossible to get an exact reading of CPU consumption: the readings at the ATX12V aren’t 100% comparable from one platform to another and the reading at the socket doesn’t allow us to isolate CPU consumption entirely.
We therefore decided to use two methods to isolate processor consumption:
- Energy consumption at the ATX12V
- 90% of the difference in energy consumption between load and idle at the socket
We took this at 90% so as to exclude power supply yield. Note that while the first reading favours processors that draw a small proportion of power from the standard ATX socket, the second favours those with high energy consumption at idle. Unfortunately no method is perfect.
[ 220V wall socket ] [ ATX12V ]The Core i7 LGA 2011 is far from attaining the energy efficiency of the Core i7 LGA 1155. In fact it’s comparable to the Core i7-990X at maximum load, but down on it in light load. This is mainly due to the fact that Turbo Boost consumes more energy on the 3960X. In spite of these slightly disappointing results, the LGA 2011 is more efficient than any AMD CPU.
