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Turbo Core to Get Even More Turbo

Energy-efficiency is one of the most important characteristics of contemporary processors. Intel, for example, puts the objective of lowering the power consumption of their upcoming microarchitectures atop of the list. AMD hasn’t yet got there, and their engineers are still primarily chasing higher speeds. But it doesn’t mean that the developers didn’t pay due attention to Bulldozer’s thermal and power characteristics. On the contrary, after Llano the principally new approaches to energy-efficiency found their way into the Bulldozer processors. However in this case the developers used the freed potential not that much for energy savings, but rather for increasing the clock frequencies and thus improving the performance even more.

Of course, the finer production process did have some positive effect on the power consumption and heat dissipation readings. Bulldozer is manufactured with high-K dielectric 32 nm process, metal gate transistors and SOI technology. In other words, it is the same GlobalFoundries process that is used for Llano manufacturing. As a result the mass production eight-core Bulldozer processors maintain 1.4 V maximum core voltage.

However, the major innovation inherited from Llano is the use of power gating, which should disconnect the power from selected parts of the CPU. They allow shutting down power on selected dual-core modules and cache-memory in Bulldozer processors.

When both computational cores within one module switch to C6 power-saving mode, the module power turns off. Unfortunately, this technology cannot apply to processor cores, because there are simply no individual cores inside Bulldozer – they share some of their resources with the other cores within the same modules.

C6 power-saving modes also control the Turbo Core technology in Bulldozer processors. When at least half of Bulldozer processor modules are off and in power-saving mode, its core voltage and clock frequencies increase. This forced mode is called Max Turbo Boost.

However, there is nothing new in Max Turbo Boost mode, as AMD introduced the same automatic overclocking back in their Thuban processors on K10 microarchitecture. The principally new thing here is the All Core Boost mode, when the clock frequency may increase beyond its nominal value even when all processor cores are active. The enhanced version of Turbo Core implemented in Bulldozer processors allows them to accurately assess their actual power consumption and heat dissipation judging by the utilization level of different units. So, if according to the processor’s estimate the current power consumption and heat dissipation are well below the threshold values, the processor can increase its core voltage and clock speed even if none of the cores are in idle mode.

So, the clock frequency of Bulldozer based processors is an extremely variable value. It may change dramatically in a very large interval (up to 900 MHz) depending on the “heaviness” of the executed algorithms and on the number of active cores.

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