[PATCH 3/3] tracing: Add documentation for trace clock tai

Kurt Kanzenbach
2022-04-09T08:13:42Z

Add documentation for new introduced trace clock tai.
This clock corresponds to CLOCK_TAI.

Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
---
Documentation/trace/ftrace.rst | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index 45b8c56af67a..b37dc19e4d40 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -517,6 +517,18 @@ of ftrace. Here is a list of some of the key files:
processing should be able to handle them. See comments in the
ktime_get_boot_fast_ns() function for more information.

+ tai:
+ This is the tai clock (CLOCK_TAI) and is derived from the wall-
+ clock time. However, this clock does not experience
+ discontinuities and backwards jumps caused by NTP inserting leap
+ seconds. Since the clock access is designed for use in tracing,
+ side effects are possible. The clock access may yield wrong
+ readouts in case the internal TAI offset is updated e.g., caused
+ by setting the system time or using adjtimex() with an offset.
+ These effects are rare and post processing should be able to
+ handle them. See comments in the ktime_get_tai_fast_ns()
+ function for more information.
+
To set a clock, simply echo the clock name into this file::

# echo global > trace_clock
--
2.30.2