Commenting on some reviews of the new AMD Ryzen CPUs,AMD claims that the Windows 10 thread scheduler is operating properly for "Zen," and that the temperature reporting sensors of the new processors have an offset.
There are some reports alleging incorrect thread scheduling on the AMD Ryzen processor. AMD believes that the Windows 10 thread scheduler is operating properly, and that ther is no issue with the scheduler adversely utilizing the logical and physical configurations of the architecture. In addition, AMD says that an outdated version of the application was responsible for originating the incorrect topology data that has been widely reported in the media. Coreinfo v3.31 (or later) will produce the correct results, according to AMD. In addition, AMd says that there are no performance deltas between Windows 7 and Windows 10 on the AMD Ryzen CPU. "Any differences in performance can be more likely attributed to software architecture differences between these OSes," AMD says.
"...our analysis highlights that there are many applications that already make good use of the cores and threads in Ryzen, and there are other applications that can better utilize the topology and capabilities of our new CPU with some targaeted optimizations," AMD says.
AMD plans to further improve the Ryzen performance in certain applications.
The primary temperature reporting sensor of the AMD Ryzen processor is a sensor called "T Control," or tCTL for short. The tCTL sensor is derived from the junction (Tj) temperature - the interface point between the die and heatspreader- but according to AMD, "it may be offset on certain CPU models so that all models on the AM4 Platform have the same maximum tCTL value." This approach ensures that all AMD Ryzen processors have a consistent fan policy.
Specifically, AMD says that the AMD Ryzen 7 1700X and 1800X carry a +20°C offset between the tCTL° (reported) temperature and the actual Tj° temperature. For now, AMD says that users of the AMD Ryzen 1700X and 1800X can subtract 20°C to determine the true junction temperature of their processor. No arithmetic is required for the Ryzen 7 1700.
AMD recommends the High Performance power plan within Windows 10 for the best performance on Ryzen. The company recommends this plan for two reasons:
- Core Parking OFF: Idle CPU cores are instantaneously available for thread scheduling. In contrast, the Balanced plan aggressively places idle CPU cores into low power states. This can cause additional latency when un-parking cores to accommodate varying loads.
- Fast frequency change: The AMD Ryzen processor can alter its voltage and frequency states in the 1ms intervals natively supported by the "Zen" architecture. In contrast, the Balanced plan may take longer for voltage and frequency (V/f) changes due to software participation in power state changes.
By the first week of April, AMD intends to provide an update for AMD Ryzen processors that optimizes the power policy parameters of the Balanced plan to favor performance more consistent with the typical usage models of a desktop PC.
AMD also investigated reports of instances where SMT is producing reduced performance in a handful of games. Based on our characterization of game workloads, AMD expects that gaming applications should generally see a neutral/positive benefit from SMT. The company sees this neutral/positive behavior in a wide range of titles, including: Arma 3, Battlefield 1, Mafia III, Watch Dogs 2, Sid Meier's Civilization VI, For Honor, Hitman, Mirror's Edge Catalyst and The Division.