RWT dissects Steamroller's adaptive clocking mechanism

AMD's Steamroller processor core is found in Kaveri-based desktop chips. This latest evolution of the Bulldozer architecture features numerous tweaks to improve performance and power efficiency, some of which we discussed in our review of the A6-7600. Steamroller also includes an unique adaptive clocking mechanism meant to counter voltage droop. Details on the technology were revealed as part of the International Solid-State Circuits Conference earlier this year, and Real World Technoligies' David Kanter has posted an interesting summary of how it works.

Voltage droop in the CPU's power supply can be problematic if it causes the processor voltage to sag below the minimum level required for a given clock speed. There are numerous solutions, including capping the CPU frequency and upping the minimum CPU voltage to avoid conditions where errors could occur. Steamroller is more intelligent. It detects voltage droop in real time and "stretches" its clock cycle to compensate.

The CPU frequency effectively drops when the mechanism is engaged, but only for as long as necessary to counter the voltage droop. According to Kanter, "most real workloads lose less than 0.2% of cycles" on a Steamroller chip clocked at 3.4GHz. Adaptive clocking allows a lower minimum voltage at that speed, yielding power savings of around 13%.

Kanter delves into the specifics of how the mechanism works and how it might be applied in other products, including GPUs. He doesn't mention AMD's all-new ARM and x86 processor cores specifically, but I don't see any barriers to applying adaptive clocking to those products. The full article is definitely worth reading, and at only a page, it's easier to digest than some of Kanter's more expansive works.

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