AMD A-Series Trinity APUs Can Drop Clock-Speed Under High-Loads

From X-bit Labs: Contemporary microprocessors from AMD and Intel can dynamically change their clock-speeds in order to reduce power consumption or improve performance. Still, there are certain clock-speeds that are declared to be default and at which the chips should operate most of the time in all applications. However, it looks like under certain conditions AMD’s latest microprocessors for desktops run at lower clock-speeds, which negatively affects performance.

AMD’s latest A-series accelerated processing units code-named Trinity have default clock-speeds, idle clock-speeds as well as maximum clock-speeds that are activated only in certain cases and when the Turbo Core technology in enabled. However, it was discovered in the “Contemporary APUs: AMD Trinity vs. Intel Ivy Bridge” article, under high multi-threaded loads, Trinity drops clock-speed below base levels. For example, AMD A10-5800K APU has a base clock rate of 3.8GHz and capable of turbo-boosting to 4.2GHz, however, at high multithreaded loads the clock-speed is dropped to 3.40GHz, not to 3.80GHz as the processor’s TDP exceeds the default level. Other Trinity microprocessors behave in similar way.

During the test of AMD Trinity APUs, X-bit labs observed stable drop of clock-speed in Linpack benchmark and irregular drops in various video encoding apps, 3D renderers, etc. It is interesting to noted that the frequency never drops when Turbo Core is disabled and the processor operates at 3.80GHz all the time. As it turns out, in certain cases AMD’s chips deliver lower performance than they are supposed to.

AMD appears to know about the problem and claims that it occurs in very rare cases under loads that are not typical for client microprocessors.

“Linpack is one of the few synthetic applications that may exceed the de-rating defined for our TDP. In the synthetic instances where base frequency causes our APU to run above its TDP, the part will throttle down to a frequency below base. Similar to Intel, thermal design power (TDP) is a realistic power target for partners to use in order to provide the best balance between cost and performance. However, as stated above, some unusual and synthetic workloads can cause a thermal event where our APU briefly drops below the base frequency.

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