One of AMD’s tasks this month is to continue developing patches for the Linux kernel for next-generation AMD Zen 4 CPUs. Citing Phoronix reports, AMD has introduced a fix for Last Branch Record Extension Version 2 (LbrExtV2) to facilitate Last Branch Record functionality in the latest architecture.
LbrExtV2 is expected to be integrated into the “perf” subsystem of the current branch before the release of Linux Kernel 6.1. The merge window for Linux 6.1 will open in October 2022.
The Last Branch Record (LBR) function determines and analyzes the control flow of software by recording branch information to registers in real-time. Branch information will allow the system to decide which paths “hot code” should point to, such as compiler optimizations for a particular profile or other optimizations seen in the application.
AMD’s patchwork will allow the LbrExtV2 functionality to be incorporated into the latest “perf” subsystem in Linux and allow the observation of performance events. The new LbrExtV2 includes “LBR-Freeze-on-PMI for better correlation of PMC overflow events, new speculative information, and new hardware-based filtering support if data for specific branch types is required.” Larabel reports. The filters included in the latest branch will include “kernel only, userspace only, conditional branches, near-close calls, near-indirect calls, near-returns, near-indirect jumps, near-relative jumps, and far branches”.
