Power consumption and efficiency
Our workload for this test is encoding a video with x264, based on a command ripped straight from the x264 benchmark you'll see later. This encoding job is a two-pass process. The first pass is lightly multithread and will give us the chance to see how power consumption looks when mechanisms like Turbo and core power gating are in use. The second pass is more widely multithreaded.
We've tested all of the CPUs in our default configuration, which includes a discrete Radeon card. We've also popped out the discrete card to get a look at power consumption for the A10, Core i3, and A8-3850.
The raw plots above give us a good sense of the several things, including the huge gap in between the max power draw of the AMD and Intel solutions in the same price range.
Notice how the Core i5-3570K draws virtually the same amount of power during the lightly-threaded first stage of the encoding process and the more heavily multithreaded second stage. Presumably, that means the CPU is taking full advantage of its prescribed power envelope during both stages. The FX-8150 isn't far from that ideal, either. The FX-8350, however, draws quite a bit more power during the second stage than the first. That suggests the FX-8350 is leaving some thermal headroom on the table with its relatively conservative 4.2GHz Turbo frequency.
The FX-8350 is a sizeable chip with a hefty thermal envelope, so these results are no surprise. The basic parameters haven't changed since the FX-8150. The test system based on the closest competition, the Core i5-3470, draws over 20W less at idle and over 100W less under load than our FX-8350 test rig.
We can quantify efficiency by looking at the amount of power used, in kilojoules, during the entirety of our test period, when the chips are busy and at idle. By that measure, the FX-8350 is an improvement over the FX-8150, since it finishes its work and drops to idle sooner.
Perhaps our best measure of CPU power efficiency is task energy: the amount of energy used while encoding our video. This measure rewards CPUs for finishing the job sooner, but it doesn't account for power draw at idle.
Although one wouldn't necessarily think of a 125W processor as power-efficient, the FX-8350 requires less energy to complete this task than any AMD processor before it. This is a pretty solid step forward compared to the Bulldozer-based FX-8150, particularly since Vishera is nothing more than tweaked silicon based on the same basic architecture and built with the same 32-nm SOI fab process.
Again, the competition from Intel is vastly more efficient overall—not just the 22-nm Ivy Bridge parts, but also the 32-nm Sandy Bridge chips.
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