Power consumption and efficiency
Our workload for this test was 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.
These plots of power use during our test period give you a sense of what to expect. The wide gap between the max power ratings of the AMD APUs (100W) and the competing Intel parts (55W) is unmistakably reflected in the power-use readings we took at the wall socket.
When idling at the Windows desktop, the Trinity chips rival their Intel competition for power efficiency. Without a discrete card installed, the A10-5800K sips power at idle. That 24W number is a testament to this chip's mobile roots.
AMD's desktop APUs leave behind those mobile roots in dramatic fashion when presented with some work to do. Our A10-equipped system draws 152W at the wall socket, about 50% more than a similarly equipped system based on the fastest Ivy Bridge, the Core i7-3770K. The Core i3-3225 system's peak power draw is well under half the A10 system's.
We can quantify efficiency by looking at the amount of power used, in kilojoules, during the entirety of our test period, both when the chips are busy and at idle. By that measure, the A10-5800K system is less power efficient overall than our Llano-based A8-3850 system. Removing the discrete graphics card helps, but not nearly enough: the Core i3-3225 system with a discrete Radeon still consumes less energy over the test period than the A10 system does without a video card installed.
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.
The Trinity systems combine relatively high power draw and fairly lengthy rendering times, so their energy efficiency is among the worst of the CPUs we've tested. There's no getting around this fact. On the desktop, these chips with their 100W TDPs are a far cry from their mobile counterparts, yet they're not fast enough to conserve energy by finishing the job quickly.