We establish the package’s power consumption results by using a special sensor loop. This way, our values represent the exact amount of power that goes into the CPU and then reemerges in the form of power loss, which is to say waste heat dissipated by the cooling subsystem. We check our sensor readings using shunts and measuring overall power consumption directly at the EPS connector (current probe and direct voltage measurement).
The CPU values supplied by the voltage converters on the motherboard via HWinfo64 are sufficiently precise for our purposes, even though the measurement intervals are longer than those of our oscilloscope. We retested Intel’s Core i9-7900X after overclocking it to 4.5 GHz and added its results to the graphs to provide a fair comparison.
We need to note that AMD’s Threadripper CPUs use different partial voltages for the SOC and SMU rails at different clock rates. These partial voltages, which, again, depend on the frequency, do have an influence on the overall package’s power consumption results. AMD recommended that we use the profile included with their 32GB DDR4-3200 kit. If the memory was operated using the standard SPD values for DDR4-2133, then the power consumption would be 15W lower!Both of AMD’s CPUs are designed for a maximum power consumption of 180W at their default settings. If the memory’s overclocked, then the CPU gets 15W less, which might affect performance in usage scenarios that employ all of the cores and, consequently, get too close to the limit.
Idle Power Consumption
Compared to AMD’s Ryzen 7, the Threadripper’s idle power consumption is just over twice as high. However, Threadripper also hosts two dies instead of one, and it also hits higher clock rates under occasional loads. The overclocked version utilizes higher voltages as well, and we just mentioned the memory’s role in power consumption.
CAD Workload Power Consumption
AutoCAD 2016 rarely uses more than two or three cores for its usual tasks. In fact, most of the time it's limited to a single core. Thus, it's not surprising that the CAD power consumption only adds a maximum of 15W to the idle power numbers, especially since the latter’s not truly idle power consumption to begin with.
The two overclocked versions add another 14W, which makes for an almost 30W difference compared to the idle power consumption. And then there’s the memory, of course.
Gaming Power Consumption
When it comes to gaming, we see an issue where Threadripper’s many cores get in each others' way. Consequently, overall performance ends up lackluster. The power consumption’s on the same level as that of Intel’s Core i9-7900X, even though Skylake-X fares much better in the benchmarks. The results are similar to those we reported for the real-time 3D CAD benchmarks.
Stress Test & Maximum Power Consumption
Power consumption goes through the roof during our stress test. This is especially true for the overclocked configurations.
In the case of a stock Intel Core i9-7900X, the motherboard has to shoulder some of the blame for this. It doesn’t lower the processor’s clock rate in accordance with the rules, but leaves them at a much higher level.
AMD’s Ryzen Threadripper doesn’t have those kinds of issues. The Asus X399 ROG Zenith Extreme motherboard limits power consumption to exactly 180W, just as it should, when using the default settings. Things look a whole lot different once the processor is manually overclocked to maximize its frequency, though. The 1950X needs 1.35V to achieve 3.9 GHz. At that point, AMD's new processors join Intel's overclocked Core i9-7900X well beyond 300W.
Depending on the task, Threadripper's two dies sometimes consume more power than other processors’ single dies. This is to be expected when all cores are operating at full load. The high power consumption’s okay if it’s put in the context of correspondingly high application performance, as long as the work that’s being done has been parallelized well and the software is optimized for AMD's architecture.
Unfortunately, Threadripper's efficiency during gaming turns out to be significantly worse than Intel’s. Skylake enjoys notably higher IPC, after all. A large portion of Threadripper's higher power consumption comes simply from a baseline that notches up from Ryzen 7. Even at idle, it draws an additional 15W or so. If those 15W are subtracted from Threadripper's gaming power consumption, then the results look a lot better. It brings their lower power consumption increase compared to idle in line with their lower gaming performance.
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