Bad news for Team Red: it appears high-end AMD Ryzen desktop processors – including flagship Ryzen 9 7950X – their performance is effectively limited by a feature in Windows 11.
The feature in question is the Windows 11 thread scheduler (sometimes called the thread director) – essentially a simple background program that dictates which cores in the processor should handle each task assigned to the system. Normally this should improve performance, but the thread scheduler seems to have issues with the dual CCD setup on the Ryzen 9 7950X and 7900X.
Upgrade with SMT disabled. Disabling SMT can almost fix the performance loss. What does it mean? Perhaps reducing the game thread pool reduces the probability that 2 of the N data sharing threads are spread across different CCDs, as N / 2 by 2 is much smaller than N by 2. pic.twitter.com/nP7sVpOWCuOctober 15, 2022
To explain what this means, the new Ryzen 9 processors essentially have two CCDs (core computing arrays) that contain the cores that power the processor. Twitter user CapFrameX discovered that Windows 11’s thread scheduler had problems with the dual CCD 7950X format, reducing performance in some games by up to 30%.
Turning off the second CCD restored performance, but essentially that means you’re buying a 16-core CPU and only using eight of them. CapFrameX also showed that disabling Simultaneous Multithreading (SMT) increased gaming performance – but again that 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 is worth noting that the cheaper chips from the new AMD range – these Ryzen 5 7600X and amazing Ryzen 7 7700X – it has no effect as they only have one CCD. In our review, we have already declared the 7700X to be the best in its class and the smartest choice for the vast majority of users when it comes to price-performance ratio.
This issue has existed before: in 2021, Update 21H2 for Windows 10 included an updated performance for the Ryzen thread scheduler tank before the issue was fixed with a chipset driver update. AMD will need to act quickly to fix this issue if it is to avoid gamers drifting away from their high-end processors.
Frustratingly, this problem only came to light a few days after deploying a separate patch for Windows 11 (available to Windows Insiders) to address an existing L3 cache latency issue in Ryzen chips, which also affected performance. If we were working for AMD, we would now be sending some heavily worded e-mails to Microsoft.