Avoid upgrading to Windows 11 if you have an AMD Ryzen CPU

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Windows 11 has finally been launched and you can upgrade your PC or laptop now, but you probably shouldn’t.

During the Beta phase, I noticed surprisingly few complaints about the new OS and things were looking promising, until now.

AMD has reported some significant performance issues with AMD Ryzen CPUs and Windows 11 and this will have a very large impact for gaming.

Up to 15% drop in latency-sensitive applications such as gaming

The problem is related to the way Windows 11 handles memory.  When running specific applications under Windows 11, AMD's Ryzen processors can exhibit L3 cache latencies that are up to three times longer, giving users a 3-5% performance drop in many applications and larger performance drops of 10-15% in latency-sensitive applications.

UEFI CPPC2 Preferred Core Not Working

Some users are also experiencing issues with the UEFI CPPC2 “preferred core” feature, preventing applications from scheduling applications to AMD's fastest CPU cores. This results in sub-standard CPU performance for Windows 11 users, especially for Ryzen processors with more than eight cores. The impact of this problem is much smaller than the memory issues.

The memory performance problem will affect all applications so anyone using a Ryzen CPU should probably avoid upgrading for now. However, it will have a greater impact for gamers, as games are highly dependent on memory and cache performance and therefore it is strongly advised that any keen gamers with an AMD CPU avoid upgrading to Windows 11 for now.

AMD is working with Microsoft to address these performance issues on Windows 11 and I would expect a fix to be pushed out relatively quickly.

The exact detail of the problem is listed on the AMD support page and I have copied the information below.

AMD Windows 11 Performance Variation in Certain Applications on Compatible AMD Processors

Known Performance ChangesImpact Resolution 
Measured and functional L3 cache latency may increase by ~3X.  Applications sensitive to memory subsystem access time may be impacted. Expected performance impact of 3-5% in affected applications, 10-15% outliers possible in games commonly used for eSports. A Windows update is in development to address this issue with expected availability in October of 2021.  
UEFI CPPC2 (“preferred core”) may not preferentially schedule threads on a processor’s fastest core.Applications sensitive to the performance of one or a few CPU threads may exhibit reduced performance.Performance impact may be more detectable in >8-core processors above 65W TDP. A software update is in development to address this issue with expected availability in October of 2021.

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