timekeeping: Introduce fast accessor to clock tai

Introduce fast/NMI safe accessor to clock tai for tracing. The Linux kernel
tracing infrastructure has support for using different clocks to generat

timekeeping: Introduce fast accessor to clock tai

Introduce fast/NMI safe accessor to clock tai for tracing. The Linux kernel
tracing infrastructure has support for using different clocks to generate
timestamps for trace events. Especially in TSN networks it's useful to have TAI
as trace clock, because the application scheduling is done in accordance to the
network time, which is based on TAI. With a tai trace_clock in place, it becomes
very convenient to correlate network activity with Linux kernel application
traces.

Use the same implementation as ktime_get_boot_fast_ns() does by reading the
monotonic time and adding the TAI offset. The same limitations as for the fast
boot implementation apply. The TAI offset may change at run time e.g., by
setting the time or using adjtimex() with an offset. However, these kind of
offset changes are rare events. Nevertheless, the user has to be aware and deal
with it in post processing.

An alternative approach would be to use the same implementation as
ktime_get_real_fast_ns() does. However, this requires to add an additional u64
member to the tk_read_base struct. This struct together with a seqcount is
designed to fit into a single cache line on 64 bit architectures. Adding a new
member would violate this constraint.

Signed-off-by: Kurt Kanzenbach <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Steven Rostedt <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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docs: timekeeping: Use correct prototype for deprecated functions

Use the correct prototypes for do_gettimeofday(), getnstimeofday() and
getnstimeofday64(). All of these returned void and passed the

docs: timekeeping: Use correct prototype for deprecated functions

Use the correct prototypes for do_gettimeofday(), getnstimeofday() and
getnstimeofday64(). All of these returned void and passed the return
value by reference. This should make the documentation of their
deprecation and replacements easier to search for.

Signed-off-by: Chris Packham <[email protected]>
Acked-by: Arnd Bergmann <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jonathan Corbet <[email protected]>

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timekeeping: Boot should be boottime for coarse ns accessor

Somewhere in all the patchsets before, this cleanup got lost.

Signed-off-by: Jason A. Donenfeld <[email protected]>
Signed-off-by: Thomas G

timekeeping: Boot should be boottime for coarse ns accessor

Somewhere in all the patchsets before, this cleanup got lost.

Signed-off-by: Jason A. Donenfeld <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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timekeeping: Add missing _ns functions for coarse accessors

This further unifies the accessors for the fast and coarse functions, so
that the same types of functions are available for each. There wa

timekeeping: Add missing _ns functions for coarse accessors

This further unifies the accessors for the fast and coarse functions, so
that the same types of functions are available for each. There was also
a bit of confusion with the documentation, which prior advertised a
function that has never existed. Finally, the vanilla ktime_get_coarse()
was omitted from the API originally, so this fills this oversight.

Signed-off-by: Jason A. Donenfeld <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Arnd Bergmann <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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timekeeping: Use proper clock specifier names in functions

This makes boot uniformly boottime and tai uniformly clocktai, to
address the remaining oversights.

Signed-off-by: Jason A. Donenfeld <Jas

timekeeping: Use proper clock specifier names in functions

This makes boot uniformly boottime and tai uniformly clocktai, to
address the remaining oversights.

Signed-off-by: Jason A. Donenfeld <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Arnd Bergmann <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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Documentation: fix typo CLOCK_MONONOTNIC_COARSE

Fix typo in documentation file timekeeping.rst: CLOCK_MONONOTNIC_COARSE
should be CLOCK_MONOTONIC_COARSE.

Signed-off-by: Aurelien Thierry <aurelien.t

Documentation: fix typo CLOCK_MONONOTNIC_COARSE

Fix typo in documentation file timekeeping.rst: CLOCK_MONONOTNIC_COARSE
should be CLOCK_MONOTONIC_COARSE.

Signed-off-by: Aurelien Thierry <[email protected]>
Signed-off-by: Jonathan Corbet <[email protected]>

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Documentation: document ktime_get_*() APIs

As Dave Chinner points out, we don't have a proper documentation for the
ktime_get() family of interfaces, making it rather unclear which of the
over 30 (!

Documentation: document ktime_get_*() APIs

As Dave Chinner points out, we don't have a proper documentation for the
ktime_get() family of interfaces, making it rather unclear which of the
over 30 (!) interfaces one should actually use in a driver or elsewhere
in the kernel.

I wrote up an explanation from how I personally see the interfaces,
documenting what each of the functions do and hopefully making it a bit
clearer which should be used where.

This is the first time I tried writing .rst format documentation, so
in addition to any mistakes in the content, I probably also introduce
nonstandard formatting ;-)

I first tried to add an extra section to
Documentation/timers/timekeeping.txt, but this is currently not included
in the generated API, and it seems useful to have the API docs as part
of what gets generated in
https://www.kernel.org/doc/html/latest/core-api/index.html#core-utilities
instead, so I started a new file there.

I also considered adding the documentation inline in the
include/linux/timekeeping.h header, but couldn't figure out how to do
that in a way that would result both in helpful inline comments as
well as readable html output, so I settled for the latter, with
a small note pointing to it from the header.

Cc: Dave Chinner <[email protected]>
Cc: John Stultz <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Stephen Boyd <[email protected]>
Tested-by: Randy Dunlap <[email protected]>
Reviewed-by: Randy Dunlap <[email protected]>
Reviewed-by: Linus Walleij <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>
Signed-off-by: Jonathan Corbet <[email protected]>

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