Bad news for Team Red: It looks like AMD’s next-gen Ryzen desktop CPUs – including the flagship Ryzen 9 7950X – are having their performance effectively limited by a feature in Windows 11.
The feature in question is Windows 11’s thread scheduler (sometimes called the thread director) – essentially a simple background program that determines which cores on a CPU should handle each task given to the system. Normally this should improve performance, but it looks like the thread scheduler is having a hard time with the dual CCD setup found on the Ryzen 9 7950X and 7900X.
Update with SMT off. Disabling SMT can almost fix the performance loss. What it means? Perhaps reducing the game’s thread pool reduces the probability that 2 out of N threads sharing data are spread across different CCDs because N/2 over 2 is much smaller than N over 2. pic.twitter.com/nP7sVpOWCuOctober 15, 2022
To flesh out what this means, the new Ryzen 9 CPUs essentially have two CCDs (core compute dies) that contain the cores that power the processor. Twitter user CapFrameX discovered that the Windows 11 thread scheduler was experiencing issues with the 7950X’s dual CCD format, reducing performance in some games by up to 30%.
Disabling the second CCD brought performance back, but that essentially means you’re buying a 16-core CPU and only using eight of them. CapFrameX also demonstrated that turning off Simultaneous Multithreading (SMT) increased gaming performance – but again, that means going from 32 threads to 16, one per core instead of two.
Review: Once again, the 7700X is the best choice for gamers
It is worth noting that the cheapest chips in AMD’s new lineup – the Ryzen 5 7600X and the amazing Ryzen 7 7700X – are unaffected as they only have a single CCD. We’ve already stated in our review that the 7700X is the best of the bunch and the smartest choice for the vast majority of users when it comes to price versus performance.
This issue has happened before: in 2021, the 21H2 update for Windows 10 saw the updated Thread Scheduler Tank performance of Ryzen CPUs before the issue was fixed with a chipset driver update. AMD will need to act fast to fix this issue if it wants to prevent gamers from straying completely from their high-end processors.
Frustratingly, this issue came to light just days after a separate Windows 11 patch (available to Windows Insiders) was deployed to address an existing issue with L3 cache latency on Ryzen chips, which was also impacting performance. If we worked for AMD, we would be sending some strong-word emails to Microsoft right now.