The atrace command (and the perfetto configuration) allow listing categories to select subsets of events to be traced.
Each category can include some userspace events and some ftrace events.
It's possible to extend exiting categories (or to define new categories) from the /vendor partition in order to add hardware specific ftrace events.
Since android 14, if the file /vendor/etc/atrace/atrace_categories.txt, atrace and perfetto will consider the categories and ftrace events listed there.
The file contains a list of categories, and for each category (on the following lines, indented with one or more spaces of time), a list of ftrace events that should be enabled when the category is enabled.
Each ftrace event should be a subdirectory in /sys/kernel/tracing/events/ and should be of the form group/event. Listing a whole group is not supported, each event needs to be listed explicitly.
It is not an error if an ftrace event is listed in the file, but not present on the tracing file system.
Example:
gfx mali/gpu_power_state mali/mali_pm_status thermal_tj thermal_exynos/thermal_cpu_pressure thermal_exynos/thermal_exynos_arm_update
The file lists two categories (gfx and thermal_tj). When the gfx category is enabled, atrace (or perfetto) will enable /sys/kernel/tracing/events/mali/gpu_power_state and /sys/kernel/tracing/events/mali/mali_pm_status. When the thermal_tj category is enabled, atrace (or perfetto) will enable /sys/kernel/tracing/events/thermal_exynos/thermal_cpu_pressure and /sys/kernel/tracing/events/thermal_exynos/thermal_exynos_arm_update.
Since android 14, if the file /vendor/etc/atrace/atrace_categories.txt exists on the file system, perfetto and atrace do not query the android.hardware.atrace HAL (which is deprecated).