AMD Trinity APUs lower clock speeds when under load

The popular hardware web site X-bit Labs has recently discovered an unannounced peculiarity of the latest Trinity APUs by AMD – when under load the chips operate at a clock speed that is even lower than the nominal one which negatively affects performance.

The peculiarity was noticed by the X-bit Labs staff when testing the latest Trinity chips against Intel Ivy Bridge processors. As any other chip AMD Trinity APUs have nominal clock speeds, idle clock speeds and Turbo clock speeds that are only active during certain circumstances and when AMD Turbo Core is enabled in the system’s BIOS. Unfortunately for AMD Trinity owners though it was discovered that the Trinity chips drop their clock speeds even below the nominal speed when under full load.

For example the AMD A10-5800K APU has a default clock speed of 3.8 GHz and is capable of Turbo Boost clock speed of 4.2 GHz but during high multithreaded loads the clock speed gets lowered to 3.4 GHz and not to 3.8 GHz as the chip’s TDP exceeds the specified value. All other Trinity chips exhibit the same behavior but the really weird thing is that this phenomenon is not observed when AMD Turbo Core is disabled – in this case the A10-5800K chip operates at 3.8 GHz when under heavy load.

AMD has confirmed the issue but claims it appears only in very rare cases when the chips are under load that is 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.”, AMD said.

Source: X-bit Labs

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