Power consumption and efficiency
The workload for this test is encoding a video with x264, based on a command ripped straight from the x264 benchmark you'll see later.
The 5960X's impressive reductions in idle power consumption versus the i7-4960X come mostly courtesy of the Asus X79 motherboard on the 4960X system; it's a great board, but we've seen similarly configured X79 systems idle at around 64W. In fact, I'm a little disappointed that our 5960X system doesn't go lower at idle. Yes, it has twice as many DIMMs as our quad-core Haswell systems onboard, but I'd hoped the power savings from DDR4 might move the needle a bit more.
Now that's more like it. This drop in peak power use is an earnest improvement over the 4960X, since that Asus X79 mobo only draws more power than other boards at idle, not under load. At first, the fact that the 5960X system pulls less power than the 4960X one surprised me. After all, the 5960X has a 140W TDP, and the 4960X's peak power rating is 130W. However, the 5960X's TDP encompasses the CPU's integrated voltage regulators. On the 4960X, the VRMs are external and don't count toward the TDP, so it makes sense that the 5960X's total system power draw would be lower.
That said, this workload doesn't really engage all eight cores and 16 threads on the 5960X throughout its execution. We saw transient peaks of 130W or more during the test run, and this same system will draw as much as 163W during a 3D rendering workload.
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.
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 5960X looks pretty darned efficient overall, regardless of the fact that this isn't the ideal workload for a 16-threaded CPU. Only a couple of quad-core Haswells use less energy to complete the task—and the 5960X brings a vast improvement in efficiency over the Core i7-4960X.
Pour one out for my homies at AMD.