Intel Icelake Brings New Top-Down Performance Counters

While the Linux support for Intel's long awaited Icelake support has been out there for months and all fundamentals seemingly mature, there have been a few last-minute additions around some non-essential functionality. One of the latest Linux kernel patch series around Icelake is adding support for new Top-Down performance counters for these next-generation Intel processors.

Back to the Sandy Bridge days there have been "Top-Down" metrics for exposing CPU pipeline statistics around bottlenecks in the processor front-end, back-end, bad speculation, or retiring. Those metrics have been done using generic counters but with Icelake and Intel CPUs moving forward, there are in-hardware fixed performance counters for these metrics.

The new Top-Down metrics also allow for exposing these bottleneck metrics on a per-thread/process basis rather than just per-core. These new Icelake Top-Down metrics should certainly help developers in profiling the code using the Linux perf subsystem in looking for CPU bottlenecks.

The support didn't make it for the Linux 5.2 kernel but the patches are on the mailing list and presumably will make it into Linux 5.3 later this summer.