Articles: CPU

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Power Consumption

The Richland series are faster than the Trinity thanks to a small increase in clock rates but there are no changes on the microarchitecture level or in their manufacturing technology, so we have some apprehensions about their power draw, especially as the Trinity series were not very economical in comparison with their Intel opponents. AMD promises that the new APUs have the same power consumption, specifying their TDP at 65 and 100 watts.

To find out more about the power consumption and heat dissipation, we performed a round of special tests. The new digital power supply unit from Corsair – AX760i – allows monitoring consumed and produced electrical power, which we use actively during our power consumption tests. The graphs below (unless specified otherwise) show the full power draw of the computer (without the monitor) measured after the power supply. It is the total power consumption of all the system components. The PSU's efficiency is not taken into account. The CPUs are loaded by running the 64-bit version of LinX 0.6.4 utility with FMA instructions support (for AMD processors) and AVX instructions support (for Intel processors). Moreover, we enabled Turbo mode and all power-saving technologies to correctly measure computer's power draw in idle mode: C1E, C6, Enhanced Intel SpeedStep and AMD Cool’n’Quiet.

Intel’s LGA1155 and LGA1150 platforms are the most economical in idle mode. The Socket FM2 platform with AMD APUs needs a few watts more. There are no changes between the Trinity and Richland designs but we can note that the Richland APUs drop their clock rate to 2.0 GHz instead of 1.4 GHz when idle.

It is at full load on the x86 cores that the lower energy efficiency of the Socket FM2 platform becomes apparent. Even AMD’s 65W APUs need about 50 watts more than similar configurations with Core i3 processors that deliver the same performance. The 100W A10 and A8 series APUs are even less economical. Thus, AMD’s Socket FM2 products cannot compete with Intel CPUs in terms of computing performance per watt. Hopefully, AMD’s upcoming Kaveri design and 28nm tech process will improve this situation because the Richland is no better than its predecessor in this respect.

To show you the full picture, we carry out another test, loading both the x86 and graphics cores. We use Luxmark 2.0 in CPU+GPU mode for that.

The overall picture remains the same but we should note one thing about it. AMD’s 100W APUs require about 15 watts more under heterogeneous load than at the maximum load on their x86 cores. The 65W APUs, on the contrary, consume less. This behavior is explained by the fact that the higher temperature of the integrated graphics core turns off the Turbo technology to keep the APUs within the specified thermal thresholds. That’s why the performance of the 100W and 65W APUs from AMD at heterogeneous loads differs more than in ordinary applications.

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