AMD Releases Community Update on Several Ryzen CPU Concerns
Since AMD released the Ryzen CPUs two weeks ago there have been a host of rumors and speculations trying to explain various issues reported in reviews and by people on the Internet. Now the company has released a statement on several of these concerns via a Ryzen community update.
The first topic tackled is if there is an issue with the Windows 10 thread scheduler, which is the part of the OS that decides what CPU core, physical or logical, runs a given thread, and is also what decides to shuffle threads around to other cores. There has been speculation the scheduler is degrading performance in some cases, but after investigating these claims AMD has concluded the thread scheduler is "operating properly for Zen" and the company does not believe there is an issue with the scheduler "utilizing the logical and physical configurations of the architecture." However it was also discovered that an outdated version of Sysinternals Coreinfo utility was producing incorrect topology data for Ryzen CPUs, but version 3.31 does provide correct results. Also, if you saw reports of significant performance differences between Windows 7 and Windows 10, AMD has concluded this is not related to scheduling differences but to the different software architectures of the operating systems.
The second topic addressed concerns temperature readings. Apparently the Ryzen 7 1700X and 1800X both carry a +20 ºC offset to the reported T Control (tCTL) temperature and the actual junction temperature. The purpose of the offset is to give all Ryzen processors a consistent fan policy, but it has also confused some temperature monitoring applications that failed to subtract the offset from the tCTL measurement. The Ryzen 7 1700 (non-X) is not affected by this as it does not have a tCTL offset.
AMD has also confirmed the recommendations to use the High Performance power plan offered in Windows 10. This turns off core parking, making idle CPU cores available for the thread scheduler and allows the CPU to alter its voltage and frequency states at the 1 ms intervals Ryzen supports, while Balanced may take longer as the software tries to participate in the power state changes. An update to optimize the power policy parameters for the Balanced plan is expected by the first week of April.
Finally, there have been reports of SMT (Simultaneous Multi-threading) reducing performance in some games. AMD's expectation is that games should generally see a neutral or positive benefit from SMT being enabled, and it has been tested in various titles. For those games that have been reported as performing worse, AMD suggests this indicates opportunities to improve the codebases of these games to better address the Zen architecture. Some simple changes have already been identified to improve how a game understands Zen's core/cache topology, and there should be a status update when these are ready.