kernel/linux.git/Documentation/core-api/timekeeping.rst, branch v6.19.11

timekeeping: Introduce fast accessor to clock tai

2022-04-14T14:19:30+00:00

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 Signed-off-by: Thomas Gleixner Cc: Steven Rostedt Link: https://lore.kernel.org/r/20220414091805.89667-2-kurt@linutronix.de

docs: timekeeping: Use correct prototype for deprecated functions

2020-04-15T20:48:26+00:00

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 Acked-by: Arnd Bergmann Link: https://lore.kernel.org/r/20200414221222.23996-1-chris.packham@alliedtelesis.co.nz Signed-off-by: Jonathan Corbet

Merge tag 'docs-5.3' of git://git.lwn.net/linux

2019-07-09T19:34:26+00:00

Pull Documentation updates from Jonathan Corbet: "It's been a relatively busy cycle for docs: - A fair pile of RST conversions, many from Mauro. These create more than the usual number of simple but annoying merge conflicts with other trees, unfortunately. He has a lot more of these waiting on the wings that, I think, will go to you directly later on. - A new document on how to use merges and rebases in kernel repos, and one on Spectre vulnerabilities. - Various improvements to the build system, including automatic markup of function() references because some people, for reasons I will never understand, were of the opinion that :c:func:``function()`` is unattractive and not fun to type. - We now recommend using sphinx 1.7, but still support back to 1.4. - Lots of smaller improvements, warning fixes, typo fixes, etc" * tag 'docs-5.3' of git://git.lwn.net/linux: (129 commits) docs: automarkup.py: ignore exceptions when seeking for xrefs docs: Move binderfs to admin-guide Disable Sphinx SmartyPants in HTML output doc: RCU callback locks need only _bh, not necessarily _irq docs: format kernel-parameters -- as code Doc : doc-guide : Fix a typo platform: x86: get rid of a non-existent document Add the RCU docs to the core-api manual Documentation: RCU: Add TOC tree hooks Documentation: RCU: Rename txt files to rst Documentation: RCU: Convert RCU UP systems to reST Documentation: RCU: Convert RCU linked list to reST Documentation: RCU: Convert RCU basic concepts to reST docs: filesystems: Remove uneeded .rst extension on toctables scripts/sphinx-pre-install: fix out-of-tree build docs: zh_CN: submitting-drivers.rst: Remove a duplicated Documentation/ Documentation: PGP: update for newer HW devices Documentation: Add section about CPU vulnerabilities for Spectre Documentation: platform: Delete x86-laptop-drivers.txt docs: Note that :c:func: should no longer be used ...

timekeeping: Boot should be boottime for coarse ns accessor

2019-06-25T06:54:51+00:00

Somewhere in all the patchsets before, this cleanup got lost. Signed-off-by: Jason A. Donenfeld Signed-off-by: Thomas Gleixner Cc: Arnd Bergmann Link: https://lkml.kernel.org/r/20190624091539.13512-1-Jason@zx2c4.com

timekeeping: Add missing _ns functions for coarse accessors

2019-06-22T10:11:28+00:00

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 Signed-off-by: Thomas Gleixner Reviewed-by: Arnd Bergmann Link: https://lkml.kernel.org/r/20190621203249.3909-3-Jason@zx2c4.com

timekeeping: Use proper clock specifier names in functions

2019-06-22T10:11:27+00:00

This makes boot uniformly boottime and tai uniformly clocktai, to address the remaining oversights. Signed-off-by: Jason A. Donenfeld Signed-off-by: Thomas Gleixner Reviewed-by: Arnd Bergmann Link: https://lkml.kernel.org/r/20190621203249.3909-2-Jason@zx2c4.com

Documentation: fix typo CLOCK_MONONOTNIC_COARSE

2019-06-07T17:19:47+00:00

Fix typo in documentation file timekeeping.rst: CLOCK_MONONOTNIC_COARSE should be CLOCK_MONOTONIC_COARSE. Signed-off-by: Aurelien Thierry Signed-off-by: Jonathan Corbet

Documentation: document ktime_get_*() APIs

2018-07-23T15:16:56+00:00

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 Cc: John Stultz Cc: Thomas Gleixner Cc: Stephen Boyd Tested-by: Randy Dunlap Reviewed-by: Randy Dunlap Reviewed-by: Linus Walleij Signed-off-by: Arnd Bergmann Signed-off-by: Jonathan Corbet