Add documentation for newly introduced trace clock "tai".
This clock corresponds to CLOCK_TAI.
Signed-off-by: Kurt Kanzenbach <[email protected]>
---
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
On Thu Apr 14 2022, Bagas Sanjaya wrote:
> On 4/14/22 16:18, Kurt Kanzenbach wrote:
>> + 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.
>> +
>
> In what file are the ktime_get_tai_fast_ns() comments?
In kernel/time/timekeeping.c. That function is introduced in patch #1
and has kernel doc comments. Similar to ktime_get_boot_fast_ns().
Thanks,
Kurt
On 4/14/22 16:18, Kurt Kanzenbach wrote:
> + 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.
> +
In what file are the ktime_get_tai_fast_ns() comments?
--
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