etc it has nowhere near Intel’s track record and involvement in contributing Linux. This is evident in aspects such as certain bugs in the first two generations of Ryzens that remained unsolved because the company chose not to get involved and simply said that they could be solved through software. This lack of habit when it comes to caring about its support for Linux is also evident in the a fix for chipsets from 20 years ago that negatively affects the performance of processors based on the Zen architecture (or at least Zen 3).
The bug, originating from a 20-year-old chipset patch, was discovered by K Prateek Nayak, an AMD engineer. To be more specific, the origin is in the inclusion of ACPI support in Linux 20 years ago, when a “dummy wait operation” had to be introduced to deal with some chipsets in which the STPCLK# (stop clock) signal is not possible. in time. A wait operation is a dummy I/O read that delays the processing of further instructions until the processor comes to a complete halt.
The problem, fixed in 2002, was noted on some AMD Athlon systems with VIA chipsets, but is not known to occur on newer chipsets and configurations.So, as K Prateek Nayak explains: “Sampling certain workloads using IBS (Instruction Based Sampling) on an AMD Zen 3 system shows that a significant amount of time is spent on a dummy operation that is incorrectly counted as resident C. -State (states, in which the CPU has limited or disabled selected functions).
“The large value of the C-State residence may cause the ‘cpuidle’ governor to recommend a deeper C-State during subsequent idle instances, which initiates a vicious cycle that leads to reduced performance in workloads that rapidly switch between busy and idle phases“.
Dave Hansen, an Intel engineer contributing to Linux, modified a patch introduced 20 years ago to work only on older systems that require it, avoiding damage to newer processors. The patch has already been incorporated into Linux 6.0, so users of top-selling distributions like Arch Linux, Gentoo Fedora and openSUSE Tumbleeweed and MicroOS should get it soon. Companies like Red Hat, SUSE, and Canonical (Ubuntu) are also expected to port it into their kernel implementations, and to be ported back for deployment in at least Linux 5.15, the latest LTS release for now.
Fortunately, the bug has been fixed and the fix should reach users on supported systems via a standard update.
