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Intel Architectural LBR Support Going Into Linux 5.9
The Linux kernel has been working with the existing MSR-based LBR functionality where with the likes of the perf subsystem can be used for recording the branches taken and other control flow information exposed for analysis and profiling. Intel recently has been working on added this Architectural LBR support to the Linux kernel.
These Linux patches come after Intel detailed the "architectural" LBR back in March with their programming reference guide. Chapter 7 there details the new LBR implementation.
With the new Linux kernel patches and their Architectural LBR support, there is faster context switching thanks to XSAVES support and new MSR features, faster LBR reading, better support for LBR features without needing to know CPU model specific information, the ability to expose LBRs to guests without model-specific features, and lower overhead. Existing LBR capabilities are still maintained.
The Intel Architectural Last Branch Records functionality is wired up and as of this morning has been queued into the perf/core branch. This is where the patches will reside until this perf code is sent in for the Linux 5.9 kernel merge window in August. Linux 5.9 in turn will debut as stable in the October timeframe.