linux.git/kernel/time/Kconfig, branch v6.6.132

clocksource: Loosen clocksource watchdog constraints

2023-01-04T04:43:45+00:00

Currently, MAX_SKEW_USEC is set to 100 microseconds, which has worked
reasonably well.  However, NTP is willing to tolerate 500 microseconds
of skew per second, and a clocksource that is good enough for NTP should
be good enough for the clocksource watchdog.  The watchdog's skew is
controlled by MAX_SKEW_USEC and the CLOCKSOURCE_WATCHDOG_MAX_SKEW_US
Kconfig option.  However, these values are doubled before being associated
with a clocksource's ->uncertainty_margin, and the ->uncertainty_margin
values of the pair of clocksource's being compared are summed before
checking against the skew.

Therefore, set both MAX_SKEW_USEC and the default for the
CLOCKSOURCE_WATCHDOG_MAX_SKEW_US Kconfig option to 125 microseconds of
skew per second, resulting in 500 microseconds of skew per second in
the clocksource watchdog's skew comparison.

Suggested-by Rik van Riel 
Signed-off-by: Paul E. McKenney

context_tracking: Take idle eqs entrypoints over RCU

2022-07-05T20:32:16+00:00

The RCU dynticks counter is going to be merged into the context tracking
subsystem. Start with moving the idle extended quiescent states
entrypoints to context tracking. For now those are dumb redirections to
existing RCU calls.

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Frederic Weisbecker 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Neeraj Upadhyay 
Cc: Uladzislau Rezki 
Cc: Joel Fernandes 
Cc: Boqun Feng 
Cc: Nicolas Saenz Julienne 
Cc: Marcelo Tosatti 
Cc: Xiongfeng Wang 
Cc: Yu Liao 
Cc: Phil Auld 
Cc: Paul Gortmaker
Cc: Alex Belits 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Nicolas Saenz Julienne 
Tested-by: Nicolas Saenz Julienne

context_tracking: Split user tracking Kconfig

2022-06-30T00:04:09+00:00

Context tracking is going to be used not only to track user transitions
but also idle/IRQs/NMIs. The user tracking part will then become a
separate feature. Prepare Kconfig for that.

[ frederic: Apply Max Filippov feedback. ]

Signed-off-by: Frederic Weisbecker 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Neeraj Upadhyay 
Cc: Uladzislau Rezki 
Cc: Joel Fernandes 
Cc: Boqun Feng 
Cc: Nicolas Saenz Julienne 
Cc: Marcelo Tosatti 
Cc: Xiongfeng Wang 
Cc: Yu Liao 
Cc: Phil Auld 
Cc: Paul Gortmaker
Cc: Alex Belits 
Signed-off-by: Paul E. McKenney 
Reviewed-by: Nicolas Saenz Julienne 
Tested-by: Nicolas Saenz Julienne

clocksource: Add a Kconfig option for WATCHDOG_MAX_SKEW

2022-02-02T01:35:43+00:00

A watchdog maximum skew of 100us may still be too small for
some systems or archs. It may also be too small when some kernel
debug config options are enabled.  So add a new Kconfig option
CLOCKSOURCE_WATCHDOG_MAX_SKEW_US to allow kernel builders to have more
control on the threshold for marking clocksource as unstable.

Signed-off-by: Waiman Long 
Signed-off-by: Paul E. McKenney

Merge tag 'timers-core-2021-06-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2021-06-29T19:31:16+00:00

Pull timer updates from Thomas Gleixner:
 "Time and clocksource/clockevent related updates:

  Core changes:

   - Infrastructure to support per CPU "broadcast" devices for per CPU
     clockevent devices which stop in deep idle states. This allows us
     to utilize the more efficient architected timer on certain ARM SoCs
     for normal operation instead of permanentely using the slow to
     access SoC specific clockevent device.

   - Print the name of the broadcast/wakeup device in /proc/timer_list

   - Make the clocksource watchdog more robust against delays between
     reading the current active clocksource and the watchdog
     clocksource. Such delays can be caused by NMIs, SMIs and vCPU
     preemption.

     Handle this by reading the watchdog clocksource twice, i.e. before
     and after reading the current active clocksource. In case that the
     two watchdog reads shows an excessive time delta, the read sequence
     is repeated up to 3 times.

   - Improve the debug output and add a test module for the watchdog
     mechanism.

   - Reimplementation of the venerable time64_to_tm() function with a
     faster and significantly smaller version. Straight from the source,
     i.e. the author of the related research paper contributed this!

  Driver changes:

   - No new drivers, not even new device tree bindings!

   - Fixes, improvements and cleanups and all over the place"

* tag 'timers-core-2021-06-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (30 commits)
  time/kunit: Add missing MODULE_LICENSE()
  time: Improve performance of time64_to_tm()
  clockevents: Use list_move() instead of list_del()/list_add()
  clocksource: Print deviation in nanoseconds when a clocksource becomes unstable
  clocksource: Provide kernel module to test clocksource watchdog
  clocksource: Reduce clocksource-skew threshold
  clocksource: Limit number of CPUs checked for clock synchronization
  clocksource: Check per-CPU clock synchronization when marked unstable
  clocksource: Retry clock read if long delays detected
  clockevents: Add missing parameter documentation
  clocksource/drivers/timer-ti-dm: Drop unnecessary restore
  clocksource/arm_arch_timer: Improve Allwinner A64 timer workaround
  clocksource/drivers/arm_global_timer: Remove duplicated argument in arm_global_timer
  clocksource/drivers/arm_global_timer: Make symbol 'gt_clk_rate_change_nb' static
  arm: zynq: don't disable CONFIG_ARM_GLOBAL_TIMER due to CONFIG_CPU_FREQ anymore
  clocksource/drivers/arm_global_timer: Implement rate compensation whenever source clock changes
  clocksource/drivers/ingenic: Rename unreasonable array names
  clocksource/drivers/timer-ti-dm: Save and restore timer TIOCP_CFG
  clocksource/drivers/mediatek: Ack and disable interrupts on suspend
  clocksource/drivers/samsung_pwm: Constify source IO memory
  ...

time: Improve performance of time64_to_tm()

2021-06-24T09:51:59+00:00

The current implementation of time64_to_tm() contains unnecessary loops,
branches and look-up tables. The new one uses an arithmetic-based algorithm
appeared in [1] and is approximately 3x faster (YMMV).

The drawback is that the new code isn't intuitive and contains many 'magic
numbers' (not unusual for this type of algorithm). However, [1] justifies
all those numbers and, given this function's history, the code is unlikely
to need much maintenance, if any at all.

Add a KUnit test for it which checks every day in a 160,000 years interval
centered at 1970-01-01 against the expected result.

[1] Neri, Schneider, "Euclidean Affine Functions and Applications to
Calendar Algorithms". https://arxiv.org/abs/2102.06959

Signed-off-by: Cassio Neri 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210622213616.313046-1-cassio.neri@gmail.com

tick/nohz: Update nohz_full Kconfig help

2021-05-13T12:21:21+00:00

CONFIG_NO_HZ_FULL behaves just like CONFIG_NO_HZ_IDLE by default.
Reassure distros about it.

Signed-off-by: Frederic Weisbecker 
Signed-off-by: Ingo Molnar 
Acked-by: Peter Zijlstra 
Link: https://lore.kernel.org/r/20210512232924.150322-6-frederic@kernel.org

Merge tag 'timers-urgent-2020-12-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2020-12-27T17:03:41+00:00

Pull timer fixes from Ingo Molnar:
 "Update/fix two CPU sanity checks in the hotplug and the boot code, and
  fix a typo in the Kconfig help text.

  [ Context: the first two commits are the result of an ongoing
    annotation+review work of (intentional) tick_do_timer_cpu() data
    races reported by KCSAN, but the annotations aren't fully cooked
    yet ]"

* tag 'timers-urgent-2020-12-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  timekeeping: Fix spelling mistake in Kconfig "fullfill" -> "fulfill"
  tick/sched: Remove bogus boot "safety" check
  tick: Remove pointless cpu valid check in hotplug code

timekeeping: Fix spelling mistake in Kconfig "fullfill" -> "fulfill"

2020-12-18T22:15:00+00:00

There is a spelling mistake in the Kconfig help text. Fix it.

Signed-off-by: Colin Ian King 
Signed-off-by: Thomas Gleixner 
Acked-by: Linus Walleij 
Link: https://lore.kernel.org/r/20201217171705.57586-1-colin.king@canonical.com

timekeeping: default GENERIC_CLOCKEVENTS to enabled

2020-10-30T20:57:07+00:00

Almost all machines use GENERIC_CLOCKEVENTS, so it feels wrong to
require each one to select that symbol manually.

Instead, enable it whenever CONFIG_LEGACY_TIMER_TICK is disabled as
a simplification. It should be possible to select both
GENERIC_CLOCKEVENTS and LEGACY_TIMER_TICK from an architecture now
and decide at runtime between the two.

For the clockevents arch-support.txt file, this means that additional
architectures are marked as TODO when they have at least one machine
that still uses LEGACY_TIMER_TICK, rather than being marked 'ok' when
at least one machine has been converted. This means that both m68k and
arm (for riscpc) revert to TODO.

At this point, we could just always enable CONFIG_GENERIC_CLOCKEVENTS
rather than leaving it off when not needed. I built an m68k
defconfig kernel (using gcc-10.1.0) and found that this would add
around 5.5KB in kernel image size:

   text	   data	    bss	    dec	    hex	filename
3861936	1092236	 196656	5150828	 4e986c	obj-m68k/vmlinux-no-clockevent
3866201	1093832	 196184	5156217	 4ead79	obj-m68k/vmlinux-clockevent

On Arm (MACH_RPC), that difference appears to be twice as large,
around 11KB on top of an 6MB vmlinux.

Reviewed-by: Geert Uytterhoeven 
Acked-by: Geert Uytterhoeven 
Tested-by: Geert Uytterhoeven 
Reviewed-by: Linus Walleij 
Signed-off-by: Arnd Bergmann