Windows 11 first update made AMD performance problem worse

JC Torres - Oct 14, 2021, 9:21pm CDT
Windows 11 first update made AMD performance problem worse

The rollout of Windows 11 has been relatively quiet, which isn’t surprising considering the small number of PCs that are receiving it or are compatible with it. Incompatible computers don’t even get the upgrade, so Microsoft is practically gatekeeping the upgrade anyway. That said, things aren’t as quiet over at the AMD camp with confirmed performance issues with some supported CPUs, a problem that was ironically exacerbated by Windows 11’s first Patch Tuesday.

There were two performance-related issues that AMD confirmed last week. The first is related to AMD’s “preferred core” feature that prevents certain CPUs from diverting processing threads to higher-performance CPU cores. The other saw a significant increase in latency on the usually fast L3 cache, which results in an overall lag in data read, write, and transfer speeds.

The good news is that both Microsoft and AMD have acknowledged the issues and have promised fixes as soon as possible. The bad news is that for at least one of the problems, things have just gotten worse after Microsoft rolled out Windows 11’s first set of updates. Now the L3 cache latency on affected AMD CPUs is almost three times worse than before.

According to TechPowerUp, its Windows 11 system running on an AMD Ryzen 7 2700X showed a 31.9ns latency after the patch compared to 17ns last week. The Windows 10 latency for the same processor was only 10ns for comparison. Heise echoes this observation on its Ryzen 5 5600G, with an L3 cache latency of 40ns after Patch Tuesday versus 12.4ns on Windows 10. Those might be small figures, but the compound effect on memory operations is quite substantial. According to Heise, Windows 10 had a read throughput of 333 GB/s while Windows 11 benchmarked at only 96 GB/s.

Another fix for this L3 cache problem is expected for next Tuesday’s update. AMD, on the other hand, will be rolling out its own preferred core patch on October 21. While upgrade hiccups aren’t exactly out of the ordinary, it’s still puzzling that such a severe performance bug could get past unnoticed, given Microsoft has already limited the number of supported processors for Windows 11 to a small number in the first place.

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