October 27 Updated: AMD has released a statement regarding the issues outlined below, confirming that it is investigating the issue and working to eliminate the problem. Original article follows...
Bad news for Team Red: it seems that AMD’s high-end Ryzen desktop CPUs – including the flagship Ryzen 9 7950X – are having their performance effectively throttled by a feature in Windows 11.
The feature in question is the Windows 11 thread scheduler (sometimes called a thread director) – essentially a simple background program that dictates which cores in a CPU should handle each task given to the system. Normally, this should improve performance, but it appears that the thread scheduler is having difficulties with the dual CCD configuration found in the Ryzen 9 7950X and 7900X.
Update with SMT off. Disabling SMT can almost fix the performance loss. What does the mean? Maybe reducing the thread pool of the game reduces the probability that 2 of N threads sharing data are spread across different CCDs because N/2 over 2 is much smaller than N over 2. https://t.co/vqnG79pWKB pic.twitter.com/nP7sVpOWCuOctober 15, 2022
To break down what this means, the new Ryzen 9 CPUs essentially have two CCDs (core compute dies) that contain the cores powering the processor. Twitter user CapFrameX found that the Windows 11 thread scheduler was experiencing issues with the double CCD format of the 7950X, reducing performance in some games by as much as 30%.
Disabling the second CCD brought performance back up, 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) boosted gaming performance – but again, this means going from 32 threads to 16, one per core instead of two.
Analysis: Once again, the 7700X is the best choice for gamers
It’s worth noting that the cheaper chips in AMD’s new range – the Ryzen 5 7600X and the awesome Ryzen 7 7700X – are unaffected, since they only have a single CCD. We've already declared in our review that the 7700X is the best of the bunch, and the smartest pick for the vast majority of users when it comes to price against 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 patch this problem if it wants to avoid gamers steering clear of its high-end processors completely.
Frustratingly, this issue has come to light just days after a separate Windows 11 patch (available to Windows Insiders) was deployed to resolve an existing issue with L3 cache latency in Ryzen chips, which was also impacting performance. If we worked for AMD, we’d be sending some strongly worded emails to Microsoft right now.
