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AMD SenseMI Suite & XFR
AMD's SenseMI feature suite consists of five key technologies that allow Ryzen 7 processors to adjust performance and power consumption parameters in real time.
Pure Power
According to AMD, its Zen architecture employs an array of 1000 sensors accurate to 1mA, 1mV, and 1°C. The Pure Power feature monitors these temperatures, voltages, and currents, enabling real-time adjustments based on decisions made by what company representatives describe as learning algorithms.
Those sensors feed telemetry data across the Infinity Fabric loop to the Infinity System Management Unit at 1ms intervals. The management unit analyzes that data and issues commands across the fabric to adjust voltage and frequency settings for optimal performance. AMD also notes this functionality helps manage its speculative cache features and AI-based branch prediction.
Each piece of silicon is unique, and AMD points out that its algorithms allow the processor to optimize itself based upon its own characteristics. Notably, other semiconductor vendors employ a similar technique to control the power consumption of their processors dynamically.
Precision Boost
Precision Boost adjusts the power/performance curve to optimal settings for the operating environment, much like Intel's Turbo Boost, based on information derived from Pure Power. The algorithms that control Precision Boost facilitate changes in 25 MHz steps, which is of course more granular than Turbo Boost's 100 MHz increments.
On the Ryzen 7 1800X, for example, Precision Boost increases the 3.6 GHz base frequency to 3.7 GHz across all cores, and can push two cores up to 4 GHz. This is important: whereas Intel's Turbo Boost technology varies clock rate based on the number of active cores, Precision Boost draws that distinction between two active cores and anything in excess of two cores, at which point maximum frequency drops to the all-cores number. What you end up with is a nice speed-up in lightly-threaded tasks, but less benefit than Turbo Boost as soon as a third core spins up.
XFR (eXtended Frequency Range)
AMD's eXtended Frequency Range feature allows the processor to dynamically adjust its clock rate above the stock and Precision Boost clocks based on available thermal headroom.
XFR automatically increases the Ryzen 7 1800X's Precision Boost ceiling by 100 MHz if your cooling solution can keep the CPU running below a certain threshold. We tested with Noctua's NH-U112S SE-AM4 air cooler and Corsair's H100i v2 closed-loop liquid cooler, and both perform well enough to engage XFR, allowing a 4.1 GHz peak clock rate. Unfortunately, we don't have AMD's stock heat sink/fan, so we don't know if it's beefy enough to make XFR work.
AMD claims this feature scales with air, water, and LN2 cooling, but doesn't specify if there's a maximum frequency with LN2.
Interestingly, the Precision Boost and XFR features are intertwined on our Asus Crosshair VI Hero motherboard. If you enable the "Core Performance Boost" setting, the 1800X triggers both Precision Boost and XFR frequencies based on your workload. But you cannot disable either feature independent of the other.
Neural Net Prediction & Smart Prefetch
AMD claims that its Neural Net Prediction capability describes a built-in neural network able to learn application behavior and pre-load instructions before they're needed, while Smart Prefetch learns access patterns to pre-load data into local cache.
Both features appear to be marketing-speak for AMD's perceptron branch predictor, which debuted in the Jaguar core. Of course, the company likely improved and optimized this technology for Zen, specifically, but it's not magic.
