AMD Clarifies "Best Cores" vs "Preferred Cores" Discrepancies For Ryzen CPUs

[harlan4096]

Over the last several weeks there’s been increasing discussions in the AMD enthusiast community about how the company’s new Ryzen 3000 processors interact with Windows, and in particular on how the new CPUs’ boost behaviour behaves in relation to a discrepancy between what tools such as Ryzen Master showcase as the best CPU cores, and what operating systems such as Windows interpret as being the best CPU cores. Today AMD is officially commenting on the situation and why it arises, whilst also describing what they’re doing to remedy the discrepancies in the data.

AMD’s Ryzen 3000 processor line-up based on the new Zen2 microarchitecture differs greatly in terms of frequency behaviour compared to past products. The new chips are AMD’s first products to make use of an ACPI feature called CPPC2 (Collaborative Power and Performance Control 2) which is an API interface between the chip’s firmware (Essentially the UEFI BIOS and AGESA) and an operating system such as Windows. The interface allows for the hardware to better communicate its frequency and power management characteristics and configurations to the OS, such that the OS’s software DVFS and scheduler are able to more optimally operate within the capabilities of the hardware.

AMD particularly uses the CPPC2 interface to communicate to the operating system the notion of “preferred cores”, which in essence are the CPU cores that under normal operation will be achieving the highest boost frequencies.

The issue at hand is that AMD also communicates another set of data via its own “Ryzen Master” tools and proprietary APIs, and it’s the relationship between these “best cores” and CPPC2’s “preferred cores” that caused for a bit of confusion ever since the original July launch.

AMD’s Ryzen Master overclocking application has had the unique characteristic that it was able to showcase to the user the “best cores” in a given processor. This was done by the means of a “star” and “dot” marking in the core status UI in the app – in the above example in my system, Ryzen master marks the best CPU core within a CCX with a star, and the second-best core with a dot. Furthermore, the best CPU cores in the whole processor is marked with a gold star.

Since the original launch, and AMD’s release of their SDK to allow third-party developers to poll data from AMD’s proprietary AGESA API for more detailed core information, we’ve also seen also other third-party tools such as HWInfo being able to showcase the ranking of the “best cores” in a processor. The information here essentially matches what Ryzen Master currently displays.

The Discrepancy Between Ryzen Master / SMU Data And CPPC2

The discrepancy that’s been discussed by the community in recent weeks, and that’s been prevalent since the launch of the Ryzen 3000 series in July, is that in the majority of situations and setups, the actual CPU cores that are being loaded in the operating system under single-threaded or lightly threaded workloads mostly never matched the best CPU cores as reported by Ryzen Master. This can be seen with any generic monitoring utility such as the task manager.

The discrepancy here lies in the actual mapping between the “best cores” information in Ryzen Master and the SMU APIs, and the “preferred cores” mapping that AMD’s firmware communicates via CPPC2 to the operating system.

The easiest way to actually view the configuration settings that CPPC2 communicates to Windows is to view the corresponding “Kernel-Processor-Power” System Windows Logs entries in the Windows Event Viewer, as depicted above in the screenshot.
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