When AMD’s brand-new core architecture launched in the form of the Ryzen 7 processors a couple of weeks ago, they were very well received. In the majority of benchmarks and productivity tests by reviewers the Ryzen 7 octa-cores easily outperformed similarly priced Intel processors and matched or even beat parts costing twice as much. While this marked the return of AMD to high-performance desktop computing there was a concern: a few scenarios where Ryzen 7 didn’t quite perform as many had expected. One such example of this is in gaming.
Ryzen 7 issues, or lack thereof, get an update
While Ryzen 7 offered incredible leaps over previous FX parts in gaming, many reviewers published some outlying scenarios where they couldn’t match even lower-end Intel parts. Typically these were when reviewers tested the CPU at lower resolutions to attempt to push the bottleneck to the CPU. There were even some scenarios where the Ryzen processors performed better with their SMT (two threads per core) disabled.
Many theories began to arise, from cache latency to communication between Core Complexes. One such theory alleged that the Windows 10 thread-scheduler was to blame for the reduced performance. The basis of this theory was due to the apparent reduced bandwidth / increased latency between CCX units, the thread scheduler should try to group lightly threaded workloads to a single CCX.
AMD responds
In a recent blog post on their website, AMD has responded to several points of interest about the Ryzen architecture’s performance. According to AMD, the Windows 10 thread scheduler is working correctly.
We have investigated reports alleging incorrect thread scheduling on the AMD Ryzen™ processor. Based on our findings, AMD believes that the Windows® 10 thread scheduler is operating properly for “Zen,” and we do not presently believe there is an issue with the scheduler adversely utilizing the logical and physical configurations of the architecture
AMD also states that there are opportunities where applications can receive targeted optimisations to improve performance. It is also noted by AMD that the SysInternals CoreInfo utility was in fact outdated and not properly reading the Ryzen architecture. Version 3.31 of this software will apparently offer accurate readings for Ryzen.
Temperature readings
In addition to the thread-scheduling query, AMD also pointed out that the 1800X and 1700X processors have a temperature offset of 20 degrees Celsius which is apparently designed to allow for a consistent fan policy. This offset is apparently not applied to the 1700, which explains why people were getting higher temperatures on the two higher-end models.
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 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, the AMD Ryzen™ 7 1700X and 1800X carry a +20°C offset between the tCTL° (reported) temperature and the actual Tj° temperature. In the short term, users of the AMD Ryzen™ 1700X and 1800X can simply subtract 20°C to determine the true junction temperature of their processor. No arithmetic is required for the Ryzen 7 1700. Long term, we expect temperature monitoring software to better understand our tCTL offsets to report the junction temperature automatically.
Power Plans
AMD has also stated that Ryzen 7 processors should be operated in the High performance power plan on Windows 10 for maximum performance. This is to prevent core parking (when the operating system essentially disabled a thread when it is under little to no load) and allows for Ryzen to switch voltage and clock states faster internally. Something which the Balanced performance plan apparently prevents. AMD released the following statement concerning the power plans:
In the near term, we recommend that games and other high-performance applications are complemented by the High Performance plan. 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.
Simultaneous Multi-threading
To address the other concerns where SMT was actually causing reduced performance in some games, AMD notes a few games where SMT actively has a positive effect or none at all, such titles include Battlefield 1 and The Division. For the remaining ‘outlyers’ AMD states:
For the remaining outliers, AMD again sees multiple opportunities within the codebases of specific applications to improve how this software addresses the “Zen” architecture. We have already identified some simple changes that can improve a game’s understanding of the “Zen” core/cache topology, and we intend to provide a status update to the community when they are ready.
You can read the original blog post here.