Qualcomm Datacenter Technologies L3 Cache Performance Monitoring Unit (PMU) — The Linux Kernel 5.18.5-gnu-1 documentation

# Qualcomm Datacenter Technologies L3 Cache Performance Monitoring Unit (PMU)

This driver supports the L3 cache PMUs found in Qualcomm Datacenter Technologies Centriq SoCs. The L3 cache on these SOCs is composed of multiple slices, shared by all cores within a socket. Each slice is exposed as a separate uncore perf PMU with device name l3cache_<socket>_<instance>. User space is responsible for aggregating across slices.

The driver provides a description of its available events and configuration options in sysfs, see /sys/devices/l3cache*. Given that these are uncore PMUs the driver also exposes a “cpumask” sysfs attribute which contains a mask consisting of one CPU per socket which will be used to handle all the PMU events on that socket.

The hardware implements 32bit event counters and has a flat 8bit event space exposed via the “event” format attribute. In addition to the 32bit physical counters the driver supports virtual 64bit hardware counters by using hardware counter chaining. This feature is exposed via the “lc” (long counter) format flag. E.g.:

    perf stat -e l3cache_0_0/read-miss,lc/

Given that these are uncore PMUs the driver does not support sampling, therefore “perf record” will not work. Per-task perf sessions are not supported.