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AMD FX-8150 and FX-6100, Bulldozer arrives on AM3+
by Marc Prieur
Published on December 6, 2011

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 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. This application has the additional 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 for 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 socket ]  [ ATX12V ]

The AMD FXs are more economical than the Phenom II X6s and even X4s at idle, which is a very interesting development. The Intel 1155 and 1156 platforms are however still a good deal more efficient. In low loads (1 thread), energy consumption is around the same as for the Phenom II X4s while in full load (100%) the FX-8150 consumes a good deal more.

Taking the reading at the ATX12V allows us to isolate the processor energy 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 connector. To get a totally accurate comparison however, we can compare processors using the same motherboard. The trends observed on the reading at the wall socket are indeed confirmed.

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 is 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 wall 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 socket ]  [ ATX12V ]

If we only compare the AM3/AM3+ processors between themselves, the ATX12V graph shows that energy efficiency hasn’t really improved since the Phenom IIs. With one thread, the resuts are comparable and with full occupation of the processor the Phenom II X6s still do better. As things stand, the Bulldozer architecture and CMT are not all that convincing here.

Comparison with the Intel offer shows Bulldozer up in a poor light whatever reading you use. Even in multithreaded performance, AMD is on a par with the previous LGA 1156 45nm generation and the LGA 1155 Sandy Bridge 32nms are clearly in another world.

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