linux-kernel - Re: [PATCH v2 3/3] tracing: Add documentation for trace clock tai

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Message-ID: <871qxzq4ha.fsf@kurt>
Date:   Thu, 14 Apr 2022 13:38:57 +0200
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Bagas Sanjaya <bagasdotme@...il.com>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Jonathan Corbet <corbet@....net>
Cc:     Richard Cochran <richardcochran@...il.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] tracing: Add documentation for trace clock tai

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

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