MS Releases Fix for AMD Ryzen CPUs (L3 Cache Bug) on Windows 11

Microsoft has released a fix for the L3 cache latency bug affecting all AMD Ryzen processors running Windows 11. The latest beta version of Windows 11 (released this morning), specifically Build 2200.282 includes this fix along with a bunch of other optimizations.

Earlier, the first Cumulative Update for Windows 11 had worsened the L3 latency issue on AMD Ryzen CPUs rather than fixing it. Unofficially dubbed “patch Tuesday”, Microsoft has scheduled Win 11 updates for the second Tuesday of every month. According to results posted by TPU, the L3 cache latency before the first Tuesday update was 17.1 ns. After the update, this figure grows (by more than 50%) to 31.9 ns!

This bus is known to affect all Ryzen CPUs, from the 2nd Gen Zen+ to the latest Zen 3-based Ryzen processors. The L3 cache latency deteriorates by as much as 6 times, adversely affecting the lows in games. Certain latency-sensitive games reportedly show a deficit of as much as 15% in some cases.

Known Discrepancy Impact  Fix
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. (Ultram)   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.
Source: AMD

AMD had released a statement on social media stating that patches for the two issues have been developed, and will be released soon. The patch for the Preferred Cores (UEFI-CPPC2) bug will be released on the 21st of October, while the L3 cache latency bug will be fixed via a future Windows Update scheduled to roll out on the 19th of October.

Areej Syed

Processors, PC gaming, and the past. I have written about computer hardware for over seven years with over 5000 published articles. I started during engineering college and haven't stopped since. On the side, I play RPGs like Baldur's Gate, Dragon Age, Mass Effect, Divinity, and Fallout. Contact: areejs12@hardwaretimes.com.
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