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AMD Cool 'n' Quiet, Turbo Core Impact On Linux
For those wondering about the impact that AMD's Cool 'n' Quiet and Turbo Core technologies have under Linux for the latest-generation Bulldozer processors, here are some tests illustrating the changes in performance, power consumption, and operating temperature.
Cool 'n' Quiet is AMD's CPU throttling technology to reduce the clock speed and voltage when the processor is idling or with minimal load, to ideally go through less power, reduce the heat output, and lower the fan speeds. This technology is not new at all and has been around since the original Athlon 64 series. It's been supported under Linux going back to the Linux 2.6.18 kernel and was benchmarked more than five years ago at Phoronix, but this is a modern look at the advantages (or disadvantages) of this technology when using an eight-core FX-8150 Bulldozer. Intel's equivalent to AMD CnQ is Enhanced Intel SpeedStep Technology (EIST).
Cool 'n' Quiet is about saving power and being more efficient while Turbo Core is about the opposite: maximizing performance. The Bulldozer CPUs feature Turbo Core 2.0 (Turbo Core was originally introduced with the Phenom II family). Turbo Core 2.0 allows boosting active cores on the Bulldozer processor. If less than half the cores are being utilized, a "max turbo mode" is used on all stressed cores. However, if all cores are being pushed to their limits, Turbo Core is activated but at a lower frequency than the maximum. This auto-overclocking is done automatically when needed. The AMD FX-8150 has a base frequency of 3.6GHz and can be turbo boosted up to 3.9GHz.
The AMD FX-8150 Bulldozer on the ASUS Crosshair V Formula motherboard was used for testing. Ubuntu 11.10 was employed with the Linux 3.1 kernel. The Cool 'n' Quiet and Turbo Core features were toggled from the ASUS UEFI BIOS. There are tests of No Cool 'n' Quiet, with Cool 'n' Quiet enabled, and then when Turbo Core was enabled. Besides looking at the benchmark results themselves, the CPU frequency, temperature, and power consumption were also logged by the Phoronix Test Suite in this brief demonstration.