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tracing: Add documentation for trace clock tai 

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

Link: https://lkml.kernel.org/r/20220414091805.89667-4-kurt@linutronix.de

Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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Kurt Kanzenbach 2022-04-14 11:18:05 +02:00 committed by Steven Rostedt (Google)
parent c575afe21c
commit 4d1257bbc2
1 changed files with 12 additions and 0 deletions
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Documentation/trace/ftrace.rst
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@ -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 processing should be able to handle them. See comments in the
ktime_get_boot_fast_ns() function for more information. 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:: To set a clock, simply echo the clock name into this file::
# echo global > trace_clock # echo global > trace_clock