AMD processors have up to 15% degraded performance in Windows 11, with updates to fix

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Windows 11 has two bugs that artificially degrade application performance on AMD processors. Games can slow down by up to 15%. The bugs that cause this are also in the final version, but a fix could be released later this month.

It seems that although AMD has many processors on the list hardware officially supported by Windows 11, this OS is not quite ready for them at the time of release. The company has now announced that Windows 11 has performance issues with processors, manifested by a large slowdown in L3 cache, as well as other separate issues. These are bugs that will be fixed, but only in a later update, so now the performance of the Ryzens is greatly degraded.

Microsoft released Windows 11 the day before, than was planned (as early as October 4), but it will probably take some time again before the biggest problems are picked up after this system has gotten into wider testing. Among the problems, however, is one that seems to affect all current Ryzen processors. The manufacturer AMD has now announced that it knows of a problem (perhaps on the side of the operating system, not the hardware), due to which the performance of these processors in the new OS or in some programs when running on this OS is lower than it should be. More precisely, there are at least two problems. They seem to have been known for many months, but are still waiting to be repaired.

Problem 1: L3 cache slowed down three times

First, there is a problem with the L3 cache in Windows 11 for some reason. AMD states that with Windows 11, the L3 cache of the AMD Ryzen processor has, for some reason, up to three times worse latency. This is reflected in benchmarks measuring its latency, but also in real applications that would depend on the L3 cache and the performance of the memory subsystem. Normally, the latency of L3 Cache Ryzens is somewhere around 40 CPU cycles (depending on the architecture) and AIDA64 measures it somewhere around 10 ns. In Windows 11, however, the same software measures over 30 ns (the exact number depends on the CPU frequency).

Permeability also seems to be damaged by this. According to AMD, some applications that are sensitive to cache latency may experience degraded performance, by as much as 3-5%. It can be worse in games that are more cache sensitive than most application software. According to AMD, in some eSports games, the drop in performance can be as much as 10-15%, although such poor results should be rare rather than typical.

How it is possible for the operating system to change the performance characteristics of the CPU core is not very clear. Nowhere does it seem to have published information as to the reason for this problem. If we were to guess, maybe it could be that Windows 11 somewhere for security (protection against Specter type attacks, for example) changed low-level work with memory and the methods used somehow conflict with the architecture of AMD processors, and this is reflected in the deterioration performance for memory operations passing through the L3 cache. If it was a hardware error in the processors, it doesn’t seem very likely that it would never affect previous operating systems.

Unfortunately, AMD also does not indicate which processors have these problems. According to users, this applies at least to Ryzens 5000 with Zen 3 architecture, and Ryzens 3000 with Zen 2 cores.

Problem 2: Boost and preferred kernels

In addition to the previous bug, Windows 11 has a problem with AMD processors elsewhere. Another separate bug is known in the fact that Windows 11 does not use the correct preferred kernels. Ryzeny 3000 and 5000 report to Windows which their cores are capable of reaching the highest frequencies. The purpose is for Windows to place the most powerful single-threaded tasks on these kernels. When assigned to a preferred core, the frequency will be higher and thus the single-stranded power will be higher.

The processor transmits this information via the CPPC2 interface in the UEFI firmware (see the article on Zen 2 architecture). But according to AMD, it doesn’t work on Winodws 11 for some reason, and the system probably doesn’t use the preferred kernels. This means that the frequency in single-threaded and non-threaded tasks (including benchmarks bude) will be even a few hundred MHz lower. So the performance is a few percent worse than what Windows 10 with CPPC2 would work. According to AMD, the biggest impact may be on 8, 12 and 16 thread processors and 65W versions. This is probably because higher models benefit more from lower kernels than lower models with lower ST boost cycles.

It should be fixed this month

The good news for users (and AMD), however, is that both of these phenomena are a bug that should be fixed. AMD states that in cooperation with Microsoft, patches should be released that will solve these problems. True, the wording used does not promise literally that the performance will return completely to 100%, but it probably should.

The fix for the first problem, the slow-behaving L3 cache, will take the form of a Windows update, so Microsoft will probably fix it in its code. The fix is ​​”in preparation”, but it is allegedly planned / expected to be released this month (October / October).

The fix for the second problem may no longer be provided by Microsoft, but directly by AMD within the drivers (probably the chipset drivers). This would indicate that the first issue in the press release says “Windows Update”, while the second issue will say “Software Update”. Thus, the commissioning of CPPC2 in Windows 11 will probably be done by changing the drivers and firmware interfaces that mediate between the OS and the processor or chipset. However, this update is also expected by the end of October.

So, in the end, it will not be a disaster, and once resolved, everything will work as it should. However, keep in mind that if the tested processors are already on Windows 11 now, the performance of AMD Ryzen processors will be underestimated by these errors in the results against their actual capabilities. It’s a bit silly, because the Intel Alder Lake processors will be released right at the beginning of November in turn, they directly need Windows 11 for ideal performance and will be undervalued on Windows 10. So hopefully the fixes will come out soon enough for the first Alder Lake reviews to be done correctly and fairly, and not until October 31. It may be fun to see if Intel’s marketing resists the temptation to use official performance. comparison against the competition of an uncorrected older version of Windows 11…

So it is interesting that the release of patches will take another month and it was not worth Microsoft to finish them in the first version of the released OS (true, the correction of the second bug is possible on AMD, not MS). At the same time, such a bug, which means a jump in performance regression against Windows 10, should be quickly detected during performance profiling, which would be reasonable to perform more or less all the time during development. Some reports of cache performance issues appeared on the Internet as early as June, when the first W11 insider builds were released.

Source: AMD