AMD Ryzen 5000 L3 Cache Latency Issues Persist in Windows 11 Even After Patch Fix

One of the main highlights of Windows 11 was the crippling bugs. The Ryzen CPU performance issues were some of the better-known bugs. There were two substantial issues affecting the Zen family. The first one increased the L3 cache latency. Known to affect all Ryzen CPUs, from the 2nd Gen Zen+ to the latest Zen 3-based Ryzen processors. The L3 cache latency deteriorated 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. 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 was supposed to 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.

Fast forward to the present day, and both Microsoft and AMD have already rolled out several updates to fix the L3 cache latency with Ryzen CPUs and Windows 11. However, even after the latest OS update (version KB5007215) which arrived this Tuesday, and a new chipset driver, the L3 cache latency remains far from optimal.

German outlet, Heise conducted tests with AIDA64 using a Ryzen 9 5950X and MSI B550M Mortar. The results are inconsistent and still notably slower than Windows 10 with the same system. The read and write speeds varied significantly and the copy throughput also fell off a cliff at times. The L3 cache latency has also remained higher (than Windows 10), meaning that it’ll take another round of patches from MS (or AMD) to fix the issue completely.

Windows 11: Run 1 Run 2Run 3Run 4 Windows 10
Read speed438GB/s723GB/s696GB/s777GB/s1047GB/s
Write speed578GB/s504GB/s176GB/s261GB/s680GB/s
Copy Speed218GB/s203GB/s689GB/s681GB/s912GB/s
Latency11.3 ns10.9 ns10.6 ns11.3 ns10.3 ns

Source: Heise


Computer hardware enthusiast, PC gamer, and almost an engineer. Former co-founder of Techquila (2017-2019), a fairly successful tech outlet. Been working on Hardware Times since 2019, an outlet dedicated to computer hardware and its applications.
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