perf docs: Document tool and hwmon events

Add a few paragraphs on tool and hwmon events.

Signed-off-by: Ian Rogers <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Cc: Ravi Bangoria <[email protected]>
Cc: Yoshihiro Furudera <[email protected]>
Cc: Howard Chu <[email protected]>
Cc: Ze Gao <[email protected]>
Cc: Changbin Du <[email protected]>
Cc: Junhao He <[email protected]>
Cc: Weilin Wang <[email protected]>
Cc: James Clark <[email protected]>
Cc: Oliver Upton <[email protected]>
Cc: Athira Jajeev <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Namhyung Kim <[email protected]>

Author: captain5050

tools/perf/Documentation/perf-list.txt

@@ -243,6 +243,21 @@ For accessing trace point events perf needs to have read access to
 /sys/kernel/tracing, even when perf_event_paranoid is in a relaxed
 setting.
 
+TOOL/HWMON EVENTS
+-----------------
+
+Some events don't have an associated PMU instead reading values
+available to software without perf_event_open. As these events don't
+support sampling they can only really be read by tools like perf stat.
+
+Tool events provide times and certain system parameters. Examples
+include duration_time, user_time, system_time and num_cpus_online.
+
+Hwmon events provide easy access to hwmon sysfs data typically in
+/sys/class/hwmon. This information includes temperatures, fan speeds
+and energy usage.
+
+
 TRACING
 -------