[PATCH] perf stat: document task-clock/cpu-clock in TIMINGS

[Christian Melendez <chrismelnu@gmail.com>]

task-clock/cpu-clock appear in perf stat's own example output but
were never explained in perf-stat.txt, unlike time elapsed/user/sys.
This came up unanswered on the list in 2013 and 2015 without docs
ever being added.

Link: https://patch.msgid.link/CAP-5=fV0-yvc68BUSKoSajHjHY_A6COgbEJYiFxRg+G-8LeJhQ@mail.gmail.com
Signed-off-by: Christian Melendez <chrismelnu@gmail.com>
---
 tools/perf/Documentation/perf-stat.txt | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt
index f334aabdc809..c0d6c344f9eb 100644
--- a/tools/perf/Documentation/perf-stat.txt
+++ b/tools/perf/Documentation/perf-stat.txt
@@ -621,6 +621,16 @@ user/system lands:
 
 Those times are the very same as displayed by the 'time' tool.
 
+We also display a clock-based timing metric that depends on the
+target being monitored:
+
+        83723.452481      task-clock:u (msec)       #    1.004 CPUs utilized
+
+For a single task, task-clock reports a clock count specific to that
+task. When the target is a CPU or the whole system (-a or -C),
+cpu-clock is reported instead. cpu-clock is a high-resolution per-CPU
+timer. See perf_event_open(2) for more details.
+
 CSV FORMAT
 ----------
 
@@ -671,4 +681,4 @@ that can be used for parsing.
 
 SEE ALSO
 --------
-linkperf:perf-top[1], linkperf:perf-list[1]
+linkperf:perf-top[1], linkperf:perf-list[1], perf_event_open(2)
-- 
2.34.1