This month, AMD continued its work on patches for the Linux kernel to prepare for the next-gen AMD Zen 4 CPUs. Recently, the company published fixes for the Last Branch Record Extension Version 2, or LbrExtV2, to assist with Last Branch Record capability in the newest architecture, reports Michael Larabel of the website Phoronix. The LbrExtV2 additions to the kernel's "perf" subsystem are preparing for the current branch before the newest Linux 6.1, which is still in development. The Linux 6.1 merge window officially opens at the beginning of October 2022.
AMD soon to add LbrExtV2 functionality to the Linux 6.1 kernel queue for the company's Zen 4 CPU architecture
The Last Branch Record functionality, or LBR, is "used for determining and analyzing the control flow of software by logging branch information to registers in real-time." The branch information will allow the system to decide what paths "hot code" should be directed to, such as optimizations to profile-specific compilers or other optimizations seen active in applications
AMD's patchwork will allow for the LbrExtV2 functionality to incorporate into the newest "perf" subsystem in Linux and allow for observing performance events. The new LbrExtV2 includes "LBR-Freeze-on-PMI for better correlating with PMC overflow events, new speculation information, and new hardware-based filtering support if desiring data on specific branch types." Filters included in the newest branch will consist of "kernel-only, user-space-only, conditional branches, near close calls, near indirect calls, near returns, near indirect jumps, near relative jumps, and far branches," reports Larabel.
The AMD Zen 4 Dense chiplet design is said to be implemented in the next-gen Ryzen and EPYC CPUs. The new chip will feature two different core technologies on the same chip and will be more focused on maximizing multi-threaded performance. Before the launch, AMD will utilize the Zen 4D architecture in the Bergamo lineup of server chips planned for launch in 2023.
AMD will soon submit the latest addition to the Linux kernel for review and will soon be added to the queue for Linux 6.1. Larabel states that unless any last-minute changes need to be made before the stable Linux kernel, the AMD LbrExtV2 capability will be added towards the end of the year and used in the newest AMD Zen 4 processors, which are set to release shortly.
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