tick/sched: Fix struct tick_sched doc warnings

Fix kernel-doc warnings in struct tick_sched:

tick-sched.h:103: warning: Function parameter or struct member 'idle_sleeptime_seq' not described in 'tick_sched'
tick-sched.h:104: warning: Excess struct member 'nohz_mode' description in 'tick_sched'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240331172652.14086-6-rdunlap@infradead.org

tick/sched: Fix build failure for CONFIG_NO_HZ_COMMON=n

In configurations with CONFIG_TICK_ONESHOT but no CONFIG_NO_HZ or
CONFIG_HIGH_RES_TIMERS, tick_sched_timer_dying() is stubbed out,
but still defined as a global function as well:

kernel/time/tick-sched.c:1599:6: error: redefinition of 'tick_sched_timer_dying'
1599 | void tick_sched_timer_dying(int cpu)
| ^
kernel/time/tick-sched.h:111:20: note: previous definition is here
111 | static inline void tick_sched_timer_dying(int cpu) { }
| ^

This configuration only appears with ARM CONFIG_ARCH_BCM_MOBILE,
which should not actually select CONFIG_TICK_ONESHOT.

Adjust the #ifdef for the stub to match the condition for building the
tick-sched.c file for consistency with the definition and to avoid
the build regression.

Fixes: 3aedb7fcd88a ("tick/sched: Remove useless oneshot ifdeffery")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240228123850.3499024-1-arnd@kernel.org

tick: Shut down low-res tick from dying CPU

The timekeeping duty is handed over from the outgoing CPU within stop
machine. This works well if CONFIG_NO_HZ_COMMON=n or the tick is in
high-res mode. However in low-res dynticks mode, the tick isn't
cancelled until the clockevent is shut down, which can happen later. The
tick may therefore fire again once IRQs are re-enabled on stop machine
and until IRQs are disabled for good upon the last call to idle.

That's so many opportunities for a timekeeper to go idle and the
outgoing CPU to take over that duty. This is why
tick_nohz_idle_stop_tick() is called one last time on idle if the CPU
is seen offline: so that the timekeeping duty is handed over again in
case the CPU has re-taken the duty.

This means there are two timekeeping handovers on CPU down hotplug with
different undocumented constraints and purposes:

1) A handover on stop machine for !dynticks || highres. All online CPUs
are guaranteed to be non-idle and the timekeeping duty can be safely
handed-over. The hrtimer tick is cancelled so it is guaranteed that in
dynticks mode the outgoing CPU won't take again the duty.

2) A handover on last idle call for dynticks && lowres. Setting the
duty to TICK_DO_TIMER_NONE makes sure that a CPU will take over the
timekeeping.

Prepare for consolidating the handover to a single place (the first one)
with shutting down the low-res tick as well from
tick_cancel_sched_timer() as well. This will simplify the handover and
unify the tick cancellation between high-res and low-res.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240225225508.11587-15-frederic@kernel.org

tick: Split nohz and highres features from nohz_mode

The nohz mode field tells about low resolution nohz mode or high
resolution nohz mode but it doesn't tell about high resolution non-nohz
mode.

In order to retrieve the latter state, tick_cancel_sched_timer() must
fiddle with struct hrtimer's internals to guess if the tick has been
initialized in high resolution.

Move instead the nohz mode field information into the tick flags and
provide two new bits: one to know if the tick is in nohz mode and
another one to know if the tick is in high resolution. The combination
of those two flags provides all the needed informations to determine
which of the three tick modes is running.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240225225508.11587-14-frederic@kernel.org

tick: Move individual bit features to debuggable mask accesses

The individual bitfields of struct tick_sched must be modified from
IRQs disabled places, otherwise local modifications can race due to them
sharing the same memory storage.

The recent move of the "got_idle_tick" bitfield to its own storage shows
that the use of these bitfields, as pretty as they look, can be as much
error prone.

In order to avoid future issues of the like and make sure that those
bitfields are safely accessed, move those flags to an explicit mask
along with a mutator function performing the basic IRQs disabled sanity
check.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240225225508.11587-13-frederic@kernel.org

tick: Move got_idle_tick away from common flags

tick_nohz_idle_got_tick() is called by cpuidle_reflect() within the idle
loop with interrupts enabled. This function modifies the struct
tick_sched's bitfield "got_idle_tick". However this bitfield is stored
within the same mask as other bitfields that can be modified from
interrupts.

Fortunately so far it looks like the only race that can happen is while
writing ->got_idle_tick to 0, an interrupt fires and writes the
->idle_active field to 0. It's then possible that the interrupted write
to ->got_idle_tick writes back the old value of ->idle_active back to 1.

However if that happens, the worst possible outcome is that the time
spent between that interrupt and the upcoming call to
tick_nohz_idle_exit() is accounted as idle, which is negligible quantity.

Still all the bitfield writes within this struct tick_sched's shadow
mask should be IRQ-safe. Therefore move this bitfield out to its own
storage to avoid further suprises.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240225225508.11587-12-frederic@kernel.org

tick/nohz: Remove duplicate between tick_nohz_switch_to_nohz() and tick_setup_sched_timer()

The ts->sched_timer initialization work of tick_nohz_switch_to_nohz()
is almost the same as that of tick_setup_sched_timer(), so adjust the
latter to get it reused by tick_nohz_switch_to_nohz().

This also makes the low resolution mode sched_timer benefit from the tick
skew boot option.

Signed-off-by: Peng Liu <liupeng17@lenovo.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240225225508.11587-2-frederic@kernel.org

timers/nohz: Protect idle/iowait sleep time under seqcount

Reading idle/IO sleep time (eg: from /proc/stat) can race with idle exit
updates because the state machine handling the stats is not atomic and
requires a coherent read batch.

As a result reading the sleep time may report irrelevant or backward
values.

Fix this with protecting the simple state machine within a seqcount.
This is expected to be cheap enough not to add measurable performance
impact on the idle path.

Note this only fixes reader VS writer condition partitially. A race
remains that involves remote updates of the CPU iowait task counter. It
can hardly be fixed.

Reported-by: Yu Liao <liaoyu15@huawei.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230222144649.624380-4-frederic@kernel.org

timers/nohz: Restructure and reshuffle struct tick_sched

Restructure and group fields by access in order to optimize cache
layout. While at it, also add missing kernel doc for two fields:
@last_jiffies and @idle_expires.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230222144649.624380-2-frederic@kernel.org

tick: Detect and fix jiffies update stall

On some rare cases, the timekeeper CPU may be delaying its jiffies
update duty for a while. Known causes include:

* The timekeeper is waiting on stop_machine in a MULTI_STOP_DISABLE_IRQ
or MULTI_STOP_RUN state. Disabled interrupts prevent from timekeeping
updates while waiting for the target CPU to complete its
stop_machine() callback.

* The timekeeper vcpu has VMEXIT'ed for a long while due to some overload
on the host.

Detect and fix these situations with emergency timekeeping catchups.

Original-patch-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>

timekeeping, clocksource: Fix various typos in comments

Fix ~56 single-word typos in timekeeping & clocksource code comments.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: linux-kernel@vger.kernel.org

tick/sched: Update tick_sched struct documentation

Adapt the documentation order of struct members to the effective order of
struct members and add missing descriptions.

Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: fweisbec@gmail.com
Cc: peterz@infradead.org
Link: https://lkml.kernel.org/r/20190321120921.16463-2-anna-maria@linutronix.de

nohz: Gather tick_sched booleans under a common flag field

Optimize the space and leave plenty of room for further flags.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
[ rjw: Do not use __this_cpu_read() to access tick_stopped and add
got_idle_tick to avoid overloading inidle ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

sched: idle: Select idle state before stopping the tick

In order to address the issue with short idle duration predictions
by the idle governor after the scheduler tick has been stopped,
reorder the code in cpuidle_idle_call() so that the governor idle
state selection runs before tick_nohz_idle_go_idle() and use the
"nohz" hint returned by cpuidle_select() to decide whether or not
to stop the tick.

This isn't straightforward, because menu_select() invokes
tick_nohz_get_sleep_length() to get the time to the next timer
event and the number returned by the latter comes from
__tick_nohz_idle_stop_tick(). Fortunately, however, it is possible
to compute that number without actually stopping the tick and with
the help of the existing code.

Namely, tick_nohz_get_sleep_length() can be made call
tick_nohz_next_event(), introduced earlier, to get the time to the
next non-highres timer event. If that happens, tick_nohz_next_event()
need not be called by __tick_nohz_idle_stop_tick() again.

If it turns out that the scheduler tick cannot be stopped going
forward or the next timer event is too close for the tick to be
stopped, tick_nohz_get_sleep_length() can simply return the time to
the next event currently programmed into the corresponding clock
event device.

In addition to knowing the return value of tick_nohz_next_event(),
however, tick_nohz_get_sleep_length() needs to know the time to the
next highres timer event, but with the scheduler tick timer excluded,
which can be computed with the help of hrtimer_get_next_event().

That minimum of that number and the tick_nohz_next_event() return
value is the total time to the next timer event with the assumption
that the tick will be stopped. It can be returned to the idle
governor which can use it for predicting idle duration (under the
assumption that the tick will be stopped) and deciding whether or
not it makes sense to stop the tick before putting the CPU into the
selected idle state.

With the above, the sleep_length field in struct tick_sched is not
necessary any more, so drop it.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=199227
Reported-by: Doug Smythies <dsmythies@telus.net>
Reported-by: Thomas Ilsche <thomas.ilsche@tu-dresden.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

time: tick-sched: Split tick_nohz_stop_sched_tick()

In order to address the issue with short idle duration predictions
by the idle governor after the scheduler tick has been stopped, split
tick_nohz_stop_sched_tick() into two separate routines, one computing
the time to the next timer event and the other simply stopping the
tick when the time to the next timer event is known.

Prepare these two routines to be called separately, as one of them
will be called by the idle governor in the cpuidle_select() code
path after subsequent changes.

Update the former callers of tick_nohz_stop_sched_tick() to use
the new routines, tick_nohz_next_event() and tick_nohz_stop_tick(),
instead of it and move the updates of the sleep_length field in
struct tick_sched into __tick_nohz_idle_stop_tick() as it doesn't
need to be updated anywhere else.

There should be no intentional visible changes in functionality
resulting from this change.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

License cleanup: add SPDX GPL-2.0 license identifier to files with no license

Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.

By default all files without license information are under the default
license of the kernel, which is GPL version 2.

Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.

This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.

How this work was done:

Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,

Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.

The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.

The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.

Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if <5
lines).

All documentation files were explicitly excluded.

The following heuristics were used to determine which SPDX license
identifiers to apply.

- when both scanners couldn't find any license traces, file was
considered to have no license information in it, and the top level
COPYING file license applied.

For non */uapi/* files that summary was:

SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 11139

and resulted in the first patch in this series.

If that file was a */uapi/* path one, it was "GPL-2.0 WITH
Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was:

SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 WITH Linux-syscall-note 930

and resulted in the second patch in this series.

- if a file had some form of licensing information in it, and was one
of the */uapi/* ones, it was denoted with the Linux-syscall-note if
any GPL family license was found in the file or had no licensing in
it (per prior point). Results summary:

SPDX license identifier # files
---------------------------------------------------|------
GPL-2.0 WITH Linux-syscall-note 270
GPL-2.0+ WITH Linux-syscall-note 169
((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21
((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17
LGPL-2.1+ WITH Linux-syscall-note 15
GPL-1.0+ WITH Linux-syscall-note 14
((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5
LGPL-2.0+ WITH Linux-syscall-note 4
LGPL-2.1 WITH Linux-syscall-note 3
((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3
((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1

and that resulted in the third patch in this series.

- when the two scanners agreed on the detected license(s), that became
the concluded license(s).

- when there was disagreement between the two scanners (one detected a
license but the other didn't, or they both detected different
licenses) a manual inspection of the file occurred.

- In most cases a manual inspection of the information in the file
resulted in a clear resolution of the license that should apply (and
which scanner probably needed to revisit its heuristics).

- When it was not immediately clear, the license identifier was
confirmed with lawyers working with the Linux Foundation.

- If there was any question as to the appropriate license identifier,
the file was flagged for further research and to be revisited later
in time.

In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.

Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights. The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.

Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.

In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.

Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
- a full scancode scan run, collecting the matched texts, detected
license ids and scores
- reviewing anything where there was a license detected (about 500+
files) to ensure that the applied SPDX license was correct
- reviewing anything where there was no detection but the patch license
was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
SPDX license was correct

This produced a worksheet with 20 files needing minor correction. This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.

These .csv files were then reviewed by Greg. Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected. This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.) Finally Greg ran the script using the .csv files to
generate the patches.

Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

nohz: Fix collision between tick and other hrtimers, again

This restores commit:

24b91e360ef5: ("nohz: Fix collision between tick and other hrtimers")

... which got reverted by commit:

558e8e27e73f: ('Revert "nohz: Fix collision between tick and other hrtimers"')

... due to a regression where CPUs spuriously stopped ticking.

The bug happened when a tick fired too early past its expected expiration:
on IRQ exit the tick was scheduled again to the same deadline but skipped
reprogramming because ts->next_tick still kept in cache the deadline.
This has been fixed now with resetting ts->next_tick from the tick
itself. Extra care has also been taken to prevent from obsolete values
throughout CPU hotplug operations.

When the tick is stopped and an interrupt occurs afterward, we check on
that interrupt exit if the next tick needs to be rescheduled. If it
doesn't need any update, we don't want to do anything.

In order to check if the tick needs an update, we compare it against the
clockevent device deadline. Now that's a problem because the clockevent
device is at a lower level than the tick itself if it is implemented
on top of hrtimer.

Every hrtimer share this clockevent device. So comparing the next tick
deadline against the clockevent device deadline is wrong because the
device may be programmed for another hrtimer whose deadline collides
with the tick. As a result we may end up not reprogramming the tick
accidentally.

In a worst case scenario under full dynticks mode, the tick stops firing
as it is supposed to every 1hz, leaving /proc/stat stalled:

Task in a full dynticks CPU
----------------------------

* hrtimer A is queued 2 seconds ahead
* the tick is stopped, scheduled 1 second ahead
* tick fires 1 second later
* on tick exit, nohz schedules the tick 1 second ahead but sees
the clockevent device is already programmed to that deadline,
fooled by hrtimer A, the tick isn't rescheduled.
* hrtimer A is cancelled before its deadline
* tick never fires again until an interrupt happens...

In order to fix this, store the next tick deadline to the tick_sched
local structure and reuse that value later to check whether we need to
reprogram the clock after an interrupt.

On the other hand, ts->sleep_length still wants to know about the next
clock event and not just the tick, so we want to improve the related
comment to avoid confusion.

Reported-and-tested-by: Tim Wright <tim@binbash.co.uk>
Reported-and-tested-by: Pavel Machek <pavel@ucw.cz>
Reported-by: James Hartsock <hartsjc@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1492783255-5051-2-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Revert "nohz: Fix collision between tick and other hrtimers"

This reverts commit 24b91e360ef521a2808771633d76ebc68bd5604b and commit
7bdb59f1ad47 ("tick/nohz: Fix possible missing clock reprog after tick
soft restart") that depends on it,

Pavel reports that it causes occasional boot hangs for him that seem to
depend on just how the machine was booted. In particular, his machine
hangs at around the PCI fixups of the EHCI USB host controller, but only
hangs from cold boot, not from a warm boot.

Thomas Gleixner suspecs it's a CPU hotplug interaction, particularly
since Pavel also saw suspend/resume issues that seem to be related.
We're reverting for now while trying to figure out the root cause.

Reported-bisected-and-tested-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org # reverted commits were marked for stable
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

nohz: Fix collision between tick and other hrtimers

When the tick is stopped and an interrupt occurs afterward, we check on
that interrupt exit if the next tick needs to be rescheduled. If it
doesn't need any update, we don't want to do anything.

In order to check if the tick needs an update, we compare it against the
clockevent device deadline. Now that's a problem because the clockevent
device is at a lower level than the tick itself if it is implemented
on top of hrtimer.

Every hrtimer share this clockevent device. So comparing the next tick
deadline against the clockevent device deadline is wrong because the
device may be programmed for another hrtimer whose deadline collides
with the tick. As a result we may end up not reprogramming the tick
accidentally.

In a worst case scenario under full dynticks mode, the tick stops firing
as it is supposed to every 1hz, leaving /proc/stat stalled:

Task in a full dynticks CPU
----------------------------

* hrtimer A is queued 2 seconds ahead
* the tick is stopped, scheduled 1 second ahead
* tick fires 1 second later
* on tick exit, nohz schedules the tick 1 second ahead but sees
the clockevent device is already programmed to that deadline,
fooled by hrtimer A, the tick isn't rescheduled.
* hrtimer A is cancelled before its deadline
* tick never fires again until an interrupt happens...

In order to fix this, store the next tick deadline to the tick_sched
local structure and reuse that value later to check whether we need to
reprogram the clock after an interrupt.

On the other hand, ts->sleep_length still wants to know about the next
clock event and not just the tick, so we want to improve the related
comment to avoid confusion.

Reported-by: James Hartsock <hartsjc@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: Wanpeng Li <wanpeng.li@hotmail.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Rik van Riel <riel@redhat.com>
Link: http://lkml.kernel.org/r/1483539124-5693-1-git-send-email-fweisbec@gmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

timers/nohz: Convert tick dependency mask to atomic_t

The tick dependency mask was intially unsigned long because this is the
type on which clear_bit() operates on and fetch_or() accepts it.

But now that we have atomic_fetch_or(), we can instead use
atomic_andnot() to clear the bit. This consolidates the type of our
tick dependency mask, reduce its size on structures and benefit from
possible architecture optimizations on atomic_t operations.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1458830281-4255-3-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

nohz: New tick dependency mask

The tick dependency is evaluated on every IRQ and context switch. This
consists is a batch of checks which determine whether it is safe to
stop the tick or not. These checks are often split in many details:
posix cpu timers, scheduler, sched clock, perf events.... each of which
are made of smaller details: posix cpu timer involves checking process
wide timers then thread wide timers. Perf involves checking freq events
then more per cpu details.

Checking these informations asynchronously every time we update the full
dynticks state bring avoidable overhead and a messy layout.

Let's introduce instead tick dependency masks: one for system wide
dependency (unstable sched clock, freq based perf events), one for CPU
wide dependency (sched, throttling perf events), and task/signal level
dependencies (posix cpu timers). The subsystems are responsible
for setting and clearing their dependency through a set of APIs that will
take care of concurrent dependency mask modifications and kick targets
to restart the relevant CPU tick whenever needed.

This new dependency engine stays beside the old one until all subsystems
having a tick dependency are converted to it.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

tick/broadcast: Make idle check independent from mode and config

Currently the broadcast busy check, which prevents the idle code from
going into deep idle, works only in one shot mode.

If NOHZ and HIGHRES are off (config or command line) there is no
sanity check at all, so under certain conditions cpus are allowed to
go into deep idle, where the local timer stops, and are not woken up
again because there is no broadcast timer installed or a hrtimer based
broadcast device is not evaluated.

Move tick_broadcast_oneshot_control() into the common code and provide
proper subfunctions for the various config combinations.

The common check in tick_broadcast_oneshot_control() is for the C3STOP
misfeature flag of the local clock event device. If its not set, idle
can proceed. If set, further checks are necessary.

Provide checks for the trivial cases:

- If broadcast is disabled in the config, then return busy

- If oneshot mode (NOHZ/HIGHES) is disabled in the config, return
busy if the broadcast device is hrtimer based.

- If oneshot mode is enabled in the config call the original
tick_broadcast_oneshot_control() function. That function needs
extra checks which will be implemented in seperate patches.

[ Split out from a larger combo patch ]

Reported-and-tested-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Suzuki Poulose <Suzuki.Poulose@arm.com>
Cc: Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>
Cc: Catalin Marinas <Catalin.Marinas@arm.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1507070929360.3916@nanos

tick: Nohz: Rework next timer evaluation

The evaluation of the next timer in the nohz code is based on jiffies
while all the tick internals are nano seconds based. We have also to
convert hrtimer nanoseconds to jiffies in the !highres case. That's
just wrong and introduces interesting corner cases.

Turn it around and convert the next timer wheel timer expiry and the
rcu event to clock monotonic and base all calculations on
nanoseconds. That identifies the case where no timer is pending
clearly with an absolute expiry value of KTIME_MAX.

Makes the code more readable and gets rid of the jiffies magic in the
nohz code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Link: http://lkml.kernel.org/r/20150414203502.184198593@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arm/bL_switcher: Kill tick suspend hackery

Use the new tick_suspend/resume_local() and get rid of the
homebrewn implementation of these in the ARM bL switcher. The
check for the cpumask is completely pointless. There is no harm
to suspend a per cpu tick device unconditionally. If that's a
real issue then we fix it proper at the core level and not with
some completely undocumented hacks in some random core code.

Move the tick internals to the core code, now that this nuisance
is gone.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[ rjw: Rebase, changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Link: http://lkml.kernel.org/r/1655112.Ws17YsMfN7@vostro.rjw.lan
Signed-off-by: Ingo Molnar <mingo@kernel.org>

tick: Move core only declarations and functions to core

No point to expose everything to the world. People just believe
such functions can be abused for whatever purposes. Sigh.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[ Rebased on top of 4.0-rc5 ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Nicolas Pitre <nico@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/28017337.VbCUc39Gme@vostro.rjw.lan
[ Merged to latest timers/core ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>