The Linux kernel Performance Events changes were merged for the newly-opened [1]Linux 6.16 cycle. Most notable are some new additions on the Intel side while AMD also saw a few changes too.

For the performance events monitoring code within the Linux kernel, the Intel CPU specific code has introduced support for Intel's Auto Count Reload "ACR" feature. Intel engineer Kan Liang explains in the patch series for Auto Count Reload the feature as:

"The relative rates among two or more events are useful for performance analysis, e.g., a high branch miss rate may indicate a performance issue. Usually, the samples with a relative rate that exceeds some threshold are more useful. However, the traditional sampling takes samples of events separately. To get the relative rates among two or more events, a high sample rate is required, which can bring high overhead. Many samples taken in the non-hotspot area are also dropped (useless) in the post-process.

The auto counter reload (ACR) feature takes samples when the relative rate of two or more events exceeds some threshold, which provides the fine-grained information at a low cost."

The other notable Intel addition is adding support for the PMU found within the next-gen Xeon "Clearwater Forest" processors. The PMU of Clearwater Forest is similar to that of current Xeon Sierra Forest processors. New for Clearwater Forest is the ARCH Process Event-Based Sampling (TPEBS) feature and some minor additions around the Darkmont X cores.

On the AMD side are a few minor driver improvements. The common Linux core code around performance events is adding support for dynamic constraints and other changes. More details on the Linux 6.16 performance events changes via [2]this merge request that has already landed in Linux Git.



[1] https://www.phoronix.com/search/Linux+6.16

[2] https://lore.kernel.org/lkml/aDLjswBHxzKz1gx2@gmail.com/