While testing AMD's A10-5800K APU, Xbitlabs.com discovered a rahter interesting thing that might be a real problem for AMD APUs as, at least some of them, might have a problem related to the TDP and downclocking.

According to Xbitlabs.com, their AMD A10-5800K sample was behaving rather strangely and in some screnarios dropped way below its 3.8GHz base clock. As you already know the A10-5800K has a base clock of 3.8GHz while it can turbo up to 4.2GHz.

While putting the APU under high multithreaded load, the clock speed ended up at 3.4GHz, which is way below the base 3.8GHz clock. The reason apparently lies in TDP as when it exceeds its default level, the APU drops its base clock. Xbitlabs.com noticed the problem in Linpack benchmark as well as in various video encoding apps and 3D renderers showing that the APU delivered lower performance than expected. Strangely enough, the drop does not happen when APU is forced to work without AMD Turbo Core, but the APU is then locked at 3.8GHz.

According to Xbitlabs.com, AMD is quite aware of the problem but notes that it occurs in very rare cases under loads that are not typical for client microprocessors, so an average user will not notice it.

It is not a big of a deal as benchmarking will definitely put much more strain on the APU or CPU than any average user will ever do and as soon as TDP drop below the treshold it should go up to at least its base clock.

You can check out more here.

Update:

We have been contacted by AMD's Public Relations Manager, Peter Amos, stating that the graceful clock throttling via the Turbo Core Technology when TDP is exceded by benchmarks in an unrealistic scenario is indeed a good design decision rather than issue. The original Xbitlabs.com has also been updated accordingly.