AMD Posts Ryzen Community Update; Power Patch Coming

The Windows Scheduler Is Not To Blame

Ryzen’s unique cache topology and simultaneous multi-threading (SMT, which is akin to Intel’s Hyper-Threading) has led to reduced performance in many games, which AMD claimed can be fixed through updates that allow software to interact correctly with the new architecture. Many opine that the Windows scheduler is improperly assigning threads to physical and logical cores, but AMD contradicts that theory:

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.

As an extension of this investigation, we have also reviewed topology logs generated by the Sysinternals Coreinfo utility. We have determined that an outdated version of the application was responsible for originating the incorrect topology data that has been widely reported in the media.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.

We touched on the subject on the first page of our Ryzen Versus Core i7 In 11 Popular Games article. Unfortunately, there is no global fix for the scheduler, so we will have to wait for updates from each individual developer.

Windows 10 Is Great, Thanks

Many users have also recorded elevated game performance in Windows 7 compared to Windows 10, which has fanned the scheduler-theory flames. AMD also addressed the issue in its statement:

Finally, we have reviewed the limited available evidence concerning performance deltas between Windows 7 and Windows 10 on the AMD Ryzen CPU. We do not believe there is an issue with scheduling differences between the two versions of Windows. Any differences in performance can be more likely attributed to software architecture differences between these OSes.

According to AMD, the scheduler isn’t the issue, but we believe the performance delta may be due to Windows 10’s more aggressive power management policy. As we outlined in our original Ryzen 7 1800X review and backed up with testing, the Ryzen processors perform better with the high-performance power profile.

The high-performance profile shifts control of the processor power states from Windows to the CPU, thus negating the operating system’s incessant desire to park cores, which results in decreased performance. Windows 7 doesn’t appear to park cores as aggressively, which is likely contributing to increased performance in the older operating system.

Speaking Of Power Plans

AMD also touched on the performance disparity between the balanced and high-performance power plans, and the company plans to issue an update in the April time-frame to address the issue.

Users may have heard that AMD recommends the High Performance power plan within Windows 10 for the best performance on Ryzen, and indeed we do. We recommend this plan for two key 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.

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.

Of course, the real question is how the revised power plan will affect Ryzen’s power consumption and thermal profile–an issue that we’re following up with the company to ascertain. Increased power consumption and thermals inevitably lead to higher cooling requirements, and thus acoustical output from the cooling solution, so the modified power profile might have an effect on many fronts.

Speaking of Thermals

AMD also addressed Ryzen’s somewhat confusing temperature reporting.

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.

The table below serves as an example of how the tCTL sensor can be interpreted in a hypothetical scenario where a Ryzen processor is operating at 38°C.

In the near term, a bit of math will rectify the issue nicely, and we expect that software utilities will evolve over time to provide accurate measurements. Much like the issue with cache measurements, though, it might take some time for the optimizations to trickle down to us.

About That Whole Gaming Thing…

Finally, AMD posted a separate blog post outlining several steps we can take to enjoy optimized gaming performance, and although most of the optimizations are no-brainers for the enthusiast set, there are a few interesting tidbits for Ryzen users.

AMD also confirmed the fact that some games perform better with SMT disabled, which we already characterized with targeted testing in our launch piece.

All in all, it’s been a rather busy 13 days since the Ryzen launch, and we continue to test the 1700X and 1700 for our full reviews. The latest tidbits of information are coming rapidly, and we expect to learn much more in the days to come.