First Windows 11 Patch Tuesday update lowers AMD chip performance

First Windows 11 Patch Tuesday update lowers AMD chip performance

Image:
First Windows 11 Patch Tuesday update lowers AMD chip performance

The first Windows 11 update reduced Ryzen processor performance by as much as 15 per cent

Microsoft's first-ever Patch Tuesday update for Windows 11 makes the existing L3 cache latency issue for AMD Ryzen chips even worse, according to a report.

AMD disclosed the issue last week, stating that Microsoft's latest Windows OS was causing substantial performance drops in some AMD processors.

The company said Windows 11 has two separate bugs, which are reducing Ryzen processors' performance by as much as 15 per cent.

The first issue may cause L3 cache latency to triple, affecting applications that rely on fast memory performance.

The second bug is related to AMD's UEFI CPPC2 ('preferred core') feature, which directs single-threaded tasks to the fastest two cores on the chip.

AMD's support document indicated that the bugs affect all AMD chips officially compatible with Windows 11. For consumers, these processors go back to 2018's Ryzen 2000 series.

TechPowerUp tested the performance of the Zen+ based Ryzen 7 2700X with Cumulative update KB5006674 (build 22000.258), which Microsoft released on 12th October.

The 2700X L3 cache latency with the update was found to be around 39.1ns on the AIDA64 benchmark - nearly four times worse than the CPU's typical 10ns performance.

When tested on the initial Windows 11 public release, the 2700X posted L3 latency of around 17 ns.

Thankfully, Microsoft and AMD have developed patches for both issues, and will release them later this week.

A Windows update to fix the L3 cache latency issue will be rolled out on 19th October, while the Preferred Cores (UEFI-CPPC2) bug will be fixed through another update to be released on 21st October.

Microsoft patched a total of 71 security vulnerabilities in its October 2021 Patch Tuesday security update, including an actively exploited zero-day bug (CVE-2021-40449) in Win32k, and three other zero-days.

CVE-2021-40449 is a use-after-free security bug in the Win32k kernel driver, which threat actors are currently using in the wild as part of an espionage campaign targeting IT firms, defence contractors and diplomatic entities.

Russian cyber security firm Kaspersky discovered the zero-day, dubbing it 'MysterySnail'.

Kevin Breen, Director of Cyber Threat Research at Immersive Labs, said CVE-2021-40449 "should definitely be a priority to patch."

The other zero-day bugs addressed in the patch are:

"As always, you know your own risk and what assets in your organisation have the most exposure, so plan your updates accordingly," Breen said.

"One thing worth considering, especially if you have critical services that rely on uptime, is your testing or roll-back processes. We've seen several occasions where patches have unintended side effects, so take this into account in your planning process.

"We always recommend patching anything that is being actively exploited first. Priv esc vulnerabilities always score lower than remote code execution, but are more commonly used by attackers once they have that initial access, so do not let the raw CVSS score be your priority order!"