[PATCH v3 00/16] timers: Cleanup delay/sleep related mess

[PATCH v3 00/16] timers: Cleanup delay/sleep related mess

[Anna-Maria Behnsen]

Hi,

a question about which sleeping function should be used in acpi_os_sleep()
started a discussion and examination about the existing documentation and
implementation of functions which insert a sleep/delay.

The result of the discussion was, that the documentation is outdated and
the implemented fsleep() reflects the outdated documentation but doesn't
help to reflect reality which in turns leads to the queue which covers the
following things:

- Split out all timeout and sleep related functions from hrtimer.c and timer.c
  into a separate file

- Update function descriptions of sleep related functions

- Change fsleep() to reflect reality

- Rework all comments or users which obviously rely on the outdated
  documentation as they reference "Documentation/timers/timers-howto.rst"

- Update the outdated documentation and move it into a file with a self
  explaining file name (as there are no more references)

- Remove checkpatch checks which also rely on the outdated documentation

The queue is available here:

  git://git.kernel.org/pub/scm/linux/kernel/git/anna-maria/linux-devel.git timers/misc

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
---
Changes in v3:
- Add review remarks
- Split checkpatch patch: 1. Remove links to outdated documentation,
  2. Remove checks in checkpatch which rely on outdated documentation
- Link to v2: https://lore.kernel.org/r/20240911-devel-anna-maria-b4-timers-flseep-v2-0-b0d3f33ccfe0@linutronix.de

Changes in v2:
- change udelay() and ndelay() as suggested by Thomas
- Update some formatting in the new sleep_timeout.c file
- minor typo changes and other small review remarks

Thanks,

        Anna-Maria

---
Anna-Maria Behnsen (16):
      MAINTAINERS: Add missing file include/linux/delay.h
      timers: Move *sleep*() and timeout functions into a separate file
      timers: Update schedule_[hr]timeout*() related function descriptions
      timers: Rename usleep_idle_range() to usleep_range_idle()
      timers: Update function descriptions of sleep/delay related functions
      delay: Rework udelay and ndelay
      timers: Adjust flseep() to reflect reality
      mm/damon/core: Use generic upper bound recommondation for usleep_range()
      timers: Add a warning to usleep_range_state() for wrong order of arguments
      checkpatch: Remove links to outdated documentation
      regulator: core: Use fsleep() to get best sleep mechanism
      iopoll/regmap/phy/snd: Fix comment referencing outdated timer documentation
      powerpc/rtas: Use fsleep() to minimize additional sleep duration
      media: anysee: Fix and remove outdated comment
      timers/Documentation: Cleanup delay/sleep documentation
      checkpatch: Remove broken sleep/delay related checks

 Documentation/dev-tools/checkpatch.rst         |   6 -
 Documentation/timers/delay_sleep_functions.rst | 121 ++++++++
 Documentation/timers/index.rst                 |   2 +-
 Documentation/timers/timers-howto.rst          | 115 --------
 MAINTAINERS                                    |   2 +
 arch/powerpc/kernel/rtas.c                     |  21 +-
 drivers/media/usb/dvb-usb-v2/anysee.c          |  17 +-
 drivers/regulator/core.c                       |  47 +--
 include/asm-generic/delay.h                    |  96 +++++--
 include/linux/delay.h                          |  79 ++++--
 include/linux/iopoll.h                         |  52 ++--
 include/linux/phy.h                            |   9 +-
 include/linux/regmap.h                         |  38 +--
 kernel/time/Makefile                           |   2 +-
 kernel/time/hrtimer.c                          | 120 --------
 kernel/time/sleep_timeout.c                    | 377 +++++++++++++++++++++++++
 kernel/time/timer.c                            | 192 -------------
 mm/damon/core.c                                |   5 +-
 scripts/checkpatch.pl                          |  38 ---
 sound/soc/sof/ops.h                            |   8 +-
 20 files changed, 704 insertions(+), 643 deletions(-)

[PATCH v3 13/16] powerpc/rtas: Use fsleep() to minimize additional sleep duration

[Anna-Maria Behnsen]

When commit 38f7b7067dae ("powerpc/rtas: rtas_busy_delay() improvements")
was introduced, documentation about proper usage of sleep related functions
was outdated.

The commit message references the usage of a HZ=100 system. When using a
20ms sleep duration on such a system and therefore using msleep(), the
possible additional slack will be +10ms.

When the system is configured with HZ=100 the granularity of a jiffy and of
a bucket of the lowest timer wheel level is 10ms. To make sure a timer will
not expire early (when queueing of the timer races with an concurrent
update of jiffies), timers are always queued into the next bucket. This is
the reason for the maximal possible slack of 10ms.

fsleep() limits the maximal possible slack to 25% by making threshold
between usleep_range() and msleep() HZ dependent. As soon as the accuracy
of msleep() is sufficient, the less expensive timer list timer based
sleeping function is used instead of the more expensive hrtimer based
usleep_range() function. The udelay() will not be used in this specific
usecase as the lowest sleep length is larger than 1 millisecond.

Use fsleep() directly instead of using an own heuristic for the best
sleeping mechanism to use.

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
---
v2: fix typos
---
 arch/powerpc/kernel/rtas.c | 21 +++++++--------------
 1 file changed, 7 insertions(+), 14 deletions(-)

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index f7e86e09c49f..d31c9799cab2 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -1390,21 +1390,14 @@ bool __ref rtas_busy_delay(int status)
 		 */
 		ms = clamp(ms, 1U, 1000U);
 		/*
-		 * The delay hint is an order-of-magnitude suggestion, not
-		 * a minimum. It is fine, possibly even advantageous, for
-		 * us to pause for less time than hinted. For small values,
-		 * use usleep_range() to ensure we don't sleep much longer
-		 * than actually needed.
-		 *
-		 * See Documentation/timers/timers-howto.rst for
-		 * explanation of the threshold used here. In effect we use
-		 * usleep_range() for 9900 and 9901, msleep() for
-		 * 9902-9905.
+		 * The delay hint is an order-of-magnitude suggestion, not a
+		 * minimum. It is fine, possibly even advantageous, for us to
+		 * pause for less time than hinted. To make sure pause time will
+		 * not be way longer than requested independent of HZ
+		 * configuration, use fsleep(). See fsleep() for details of
+		 * used sleeping functions.
 		 */
-		if (ms <= 20)
-			usleep_range(ms * 100, ms * 1000);
-		else
-			msleep(ms);
+		fsleep(ms * 1000);
 		break;
 	case RTAS_BUSY:
 		ret = true;

-- 
2.39.5

Re: (subset) [PATCH v3 00/16] timers: Cleanup delay/sleep related mess

[Mark Brown]

On Mon, 14 Oct 2024 10:22:17 +0200, Anna-Maria Behnsen wrote:
> a question about which sleeping function should be used in acpi_os_sleep()
> started a discussion and examination about the existing documentation and
> implementation of functions which insert a sleep/delay.
> 
> The result of the discussion was, that the documentation is outdated and
> the implemented fsleep() reflects the outdated documentation but doesn't
> help to reflect reality which in turns leads to the queue which covers the
> following things:
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator.git for-next

Thanks!

[11/16] regulator: core: Use fsleep() to get best sleep mechanism
        commit: f20669fbcf99d0e15e94fb50929bb1c41618e197

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

Re: (subset) [PATCH v3 00/16] timers: Cleanup delay/sleep related mess

[Anna-Maria Behnsen]

Hi Mark,

Mark Brown <broonie@kernel.org> writes:

> On Mon, 14 Oct 2024 10:22:17 +0200, Anna-Maria Behnsen wrote:
>> a question about which sleeping function should be used in acpi_os_sleep()
>> started a discussion and examination about the existing documentation and
>> implementation of functions which insert a sleep/delay.
>> 
>> The result of the discussion was, that the documentation is outdated and
>> the implemented fsleep() reflects the outdated documentation but doesn't
>> help to reflect reality which in turns leads to the queue which covers the
>> following things:
>> 
>> [...]
>
> Applied to
>
>    https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator.git for-next
>

Would it be ok for you, if the patch is routed through tip tree? kernel
test robot triggers a warning for htmldoc that there is a reference to
the no longer existing file 'timer-howto.rst':

  https://lore.kernel.org/r/202410161059.a0f6IBwj-lkp@intel.com

Thanks,

	Anna-Maria

Re: (subset) [PATCH v3 00/16] timers: Cleanup delay/sleep related mess

[Mark Brown]

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On Fri, Oct 18, 2024 at 10:06:33AM +0200, Anna-Maria Behnsen wrote:

> Would it be ok for you, if the patch is routed through tip tree? kernel
> test robot triggers a warning for htmldoc that there is a reference to
> the no longer existing file 'timer-howto.rst':

>   https://lore.kernel.org/r/202410161059.a0f6IBwj-lkp@intel.com

It should be fine, worst case we just get a duplicate patch which
doesn't super matter.

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Re: (subset) [PATCH v3 00/16] timers: Cleanup delay/sleep related mess

[Mark Brown]

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On Fri, Oct 18, 2024 at 10:06:33AM +0200, Anna-Maria Behnsen wrote:

> Would it be ok for you, if the patch is routed through tip tree? kernel
> test robot triggers a warning for htmldoc that there is a reference to
> the no longer existing file 'timer-howto.rst':

>   https://lore.kernel.org/r/202410161059.a0f6IBwj-lkp@intel.com

Oh, and for that:

Reviewed-by: Mark Brown <broonie@kernel.org>

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