linux-toradex.git/kernel/time/hrtimer.c, branch v6.13-rc6

Merge tag 'timers-core-2024-11-18' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2024-11-20T00:35:06+00:00

Pull timer updates from Thomas Gleixner:
 "A rather large update for timekeeping and timers:

   - The final step to get rid of auto-rearming posix-timers

     posix-timers are currently auto-rearmed by the kernel when the
     signal of the timer is ignored so that the timer signal can be
     delivered once the corresponding signal is unignored.

     This requires to throttle the timer to prevent a DoS by small
     intervals and keeps the system pointlessly out of low power states
     for no value. This is a long standing non-trivial problem due to
     the lock order of posix-timer lock and the sighand lock along with
     life time issues as the timer and the sigqueue have different life
     time rules.

     Cure this by:

       - Embedding the sigqueue into the timer struct to have the same
         life time rules. Aside of that this also avoids the lookup of
         the timer in the signal delivery and rearm path as it's just a
         always valid container_of() now.

       - Queuing ignored timer signals onto a seperate ignored list.

       - Moving queued timer signals onto the ignored list when the
         signal is switched to SIG_IGN before it could be delivered.

       - Walking the ignored list when SIG_IGN is lifted and requeue the
         signals to the actual signal lists. This allows the signal
         delivery code to rearm the timer.

     This also required to consolidate the signal delivery rules so they
     are consistent across all situations. With that all self test
     scenarios finally succeed.

   - Core infrastructure for VFS multigrain timestamping

     This is required to allow the kernel to use coarse grained time
     stamps by default and switch to fine grained time stamps when inode
     attributes are actively observed via getattr().

     These changes have been provided to the VFS tree as well, so that
     the VFS specific infrastructure could be built on top.

   - Cleanup and consolidation of the sleep() infrastructure

       - Move all sleep and timeout functions into one file

       - Rework udelay() and ndelay() into proper documented inline
         functions and replace the hardcoded magic numbers by proper
         defines.

       - Rework the fsleep() implementation to take the reality of the
         timer wheel granularity on different HZ values into account.
         Right now the boundaries are hard coded time ranges which fail
         to provide the requested accuracy on different HZ settings.

       - Update documentation for all sleep/timeout related functions
         and fix up stale documentation links all over the place

       - Fixup a few usage sites

   - Rework of timekeeping and adjtimex(2) to prepare for multiple PTP
     clocks

     A system can have multiple PTP clocks which are participating in
     seperate and independent PTP clock domains. So far the kernel only
     considers the PTP clock which is based on CLOCK TAI relevant as
     that's the clock which drives the timekeeping adjustments via the
     various user space daemons through adjtimex(2).

     The non TAI based clock domains are accessible via the file
     descriptor based posix clocks, but their usability is very limited.
     They can't be accessed fast as they always go all the way out to
     the hardware and they cannot be utilized in the kernel itself.

     As Time Sensitive Networking (TSN) gains traction it is required to
     provide fast user and kernel space access to these clocks.

     The approach taken is to utilize the timekeeping and adjtimex(2)
     infrastructure to provide this access in a similar way how the
     kernel provides access to clock MONOTONIC, REALTIME etc.

     Instead of creating a duplicated infrastructure this rework
     converts timekeeping and adjtimex(2) into generic functionality
     which operates on pointers to data structures instead of using
     static variables.

     This allows to provide time accessors and adjtimex(2) functionality
     for the independent PTP clocks in a subsequent step.

   - Consolidate hrtimer initialization

     hrtimers are set up by initializing the data structure and then
     seperately setting the callback function for historical reasons.

     That's an extra unnecessary step and makes Rust support less
     straight forward than it should be.

     Provide a new set of hrtimer_setup*() functions and convert the
     core code and a few usage sites of the less frequently used
     interfaces over.

     The bulk of the htimer_init() to hrtimer_setup() conversion is
     already prepared and scheduled for the next merge window.

   - Drivers:

       - Ensure that the global timekeeping clocksource is utilizing the
         cluster 0 timer on MIPS multi-cluster systems.

         Otherwise CPUs on different clusters use their cluster specific
         clocksource which is not guaranteed to be synchronized with
         other clusters.

       - Mostly boring cleanups, fixes, improvements and code movement"

* tag 'timers-core-2024-11-18' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (140 commits)
  posix-timers: Fix spurious warning on double enqueue versus do_exit()
  clocksource/drivers/arm_arch_timer: Use of_property_present() for non-boolean properties
  clocksource/drivers/gpx: Remove redundant casts
  clocksource/drivers/timer-ti-dm: Fix child node refcount handling
  dt-bindings: timer: actions,owl-timer: convert to YAML
  clocksource/drivers/ralink: Add Ralink System Tick Counter driver
  clocksource/drivers/mips-gic-timer: Always use cluster 0 counter as clocksource
  clocksource/drivers/timer-ti-dm: Don't fail probe if int not found
  clocksource/drivers:sp804: Make user selectable
  clocksource/drivers/dw_apb: Remove unused dw_apb_clockevent functions
  hrtimers: Delete hrtimer_init_on_stack()
  alarmtimer: Switch to use hrtimer_setup() and hrtimer_setup_on_stack()
  io_uring: Switch to use hrtimer_setup_on_stack()
  sched/idle: Switch to use hrtimer_setup_on_stack()
  hrtimers: Delete hrtimer_init_sleeper_on_stack()
  wait: Switch to use hrtimer_setup_sleeper_on_stack()
  timers: Switch to use hrtimer_setup_sleeper_on_stack()
  net: pktgen: Switch to use hrtimer_setup_sleeper_on_stack()
  futex: Switch to use hrtimer_setup_sleeper_on_stack()
  fs/aio: Switch to use hrtimer_setup_sleeper_on_stack()
  ...

hrtimers: Delete hrtimer_init_on_stack()

2024-11-07T01:47:07+00:00

hrtimer_init_on_stack() is now unused. Delete it.

Signed-off-by: Nam Cao 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/all/510ce0d2944c4a382ea51e51d03dcfb73ba0f4f7.1730386209.git.namcao@linutronix.de

hrtimers: Delete hrtimer_init_sleeper_on_stack()

2024-11-07T01:47:06+00:00

hrtimer_init_sleeper_on_stack() is now unused. Delete it.

Signed-off-by: Nam Cao 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/all/52549846635c0b3a2abf82101f539efdabcd9778.1730386209.git.namcao@linutronix.de

timers: Switch to use hrtimer_setup_sleeper_on_stack()

2024-11-07T01:47:06+00:00

hrtimer_setup_sleeper_on_stack() replaces hrtimer_init_sleeper_on_stack()
to keep the naming convention consistent.

Convert the usage sites over to it. The conversion was done with
Coccinelle.

Signed-off-by: Nam Cao 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/all/299c07f0f96af8ab3a7631b47b6ca22b06b20577.1730386209.git.namcao@linutronix.de

hrtimers: Introduce hrtimer_setup_sleeper_on_stack()

2024-11-07T01:47:05+00:00

The hrtimer_init*() API is replaced by hrtimer_setup*() variants to
initialize the timer including the callback function at once.

hrtimer_init_sleeper_on_stack() does not need user to setup the callback
function separately, so a new variant would not be strictly necessary.

Nonetheless, to keep the naming convention consistent, introduce
hrtimer_setup_sleeper_on_stack(). hrtimer_init_on_stack() will be removed
once all users are converted.

Signed-off-by: Nam Cao 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/all/7b5e18e6dd0ace9eaa211201528cb9dc23752454.1730386209.git.namcao@linutronix.de

hrtimers: Introduce hrtimer_setup_on_stack()

2024-11-07T01:47:05+00:00

To initialize hrtimer on stack, hrtimer_init_on_stack() needs to be called
and also hrtimer::function must be set. This is error-prone and awkward to
use.

Introduce hrtimer_setup_on_stack() which does both of these things, so that
users of hrtimer can be simplified.

The new setup function also has a sanity check for the provided function
pointer. If NULL, a warning is emitted and a dummy callback installed.

hrtimer_init_on_stack() will be removed as soon as all of its users have
been converted to the new function.

Signed-off-by: Nam Cao 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/all/4b05e2ab3a82c517adf67fabc0f0cd8fe118b97c.1730386209.git.namcao@linutronix.de

hrtimers: Introduce hrtimer_setup() to replace hrtimer_init()

2024-11-07T01:47:05+00:00

To initialize hrtimer, hrtimer_init() needs to be called and also
hrtimer::function must be set. This is error-prone and awkward to use.

Introduce hrtimer_setup() which does both of these things, so that users of
hrtimer can be simplified.

The new setup function also has a sanity check for the provided function
pointer. If NULL, a warning is emitted and a dummy callback installed.

hrtimer_init() will be removed as soon as all of its users have been
converted to the new function.

Signed-off-by: Nam Cao 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/all/5057c1ddbfd4b92033cd93d37fe38e6b069d5ba6.1730386209.git.namcao@linutronix.de

hrtimers: Add missing hrtimer_init() trace points

2024-11-07T01:47:04+00:00

hrtimer_init*_on_stack() is not covered by tracing when
CONFIG_DEBUG_OBJECTS_TIMERS=y.

Rework the functions similar to hrtimer_init() and hrtimer_init_sleeper()
so that the hrtimer_init() tracepoint is unconditionally available.

The rework makes hrtimer_init_sleeper() unused. Delete it.

Signed-off-by: Nam Cao 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/all/74528e8abf2bb96e8bee85ffacbf14e15cf89f0d.1730386209.git.namcao@linutronix.de

softirq: Use a dedicated thread for timer wakeups on PREEMPT_RT.

2024-11-07T01:44:38+00:00

The timer and hrtimer soft interrupts are raised in hard interrupt
context. With threaded interrupts force enabled or on PREEMPT_RT this leads
to waking the ksoftirqd for the processing of the soft interrupt.

ksoftirqd runs as SCHED_OTHER task which means it will compete with other
tasks for CPU resources.  This can introduce long delays for timer
processing on heavy loaded systems and is not desired.

Split the TIMER_SOFTIRQ and HRTIMER_SOFTIRQ processing into a dedicated
timers thread and let it run at the lowest SCHED_FIFO priority.
Wake-ups for RT tasks happen from hardirq context so only timer_list timers
and hrtimers for "regular" tasks are processed here. The higher priority
ensures that wakeups are performed before scheduling SCHED_OTHER tasks.

Using a dedicated variable to store the pending softirq bits values ensure
that the timer are not accidentally picked up by ksoftirqd and other
threaded interrupts.

It shouldn't be picked up by ksoftirqd since it runs at lower priority.
However if ksoftirqd is already running while a timer fires, then ksoftird
will be PI-boosted due to the BH-lock to ktimer's priority.

The timer thread can pick up pending softirqs from ksoftirqd but only
if the softirq load is high. It is not be desired that the picked up
softirqs are processed at SCHED_FIFO priority under high softirq load
but this can already happen by a PI-boost by a force-threaded interrupt.

[ frederic@kernel.org: rcutorture.c fixes, storm fix by introduction of
  local_timers_pending() for tick_nohz_next_event() ]

[ junxiao.chang@intel.com: Ensure ktimersd gets woken up even if a
  softirq is currently served. ]

Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Paul E. McKenney  [rcutorture]
Reviewed-by: Frederic Weisbecker 
Link: https://lore.kernel.org/all/20241106150419.2593080-4-bigeasy@linutronix.de

hrtimer: Use __raise_softirq_irqoff() to raise the softirq

2024-11-07T01:44:38+00:00

Raising the hrtimer soft interrupt is always done from hard interrupt
context, so it can be reduced to just setting the HRTIMER soft interrupt
flag. The soft interrupt will be invoked on return from interrupt.

Use therefore __raise_softirq_irqoff() to raise the HRTIMER soft interrupt,
which is a trivial optimization.

Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Frederic Weisbecker 
Link: https://lore.kernel.org/all/20241106150419.2593080-2-bigeasy@linutronix.de