linux.git/kernel/time/tick-broadcast.c, branch v6.1.2

timer_list: Print name of per-cpu wakeup device

2021-05-31T15:04:49+00:00

With the introduction of per-cpu wakeup devices that can be used in
preference to the broadcast timer, print the name of such devices when
they are available.

Signed-off-by: Will Deacon 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210524221818.15850-6-will@kernel.org

tick/broadcast: Program wakeup timer when entering idle if required

2021-05-31T15:04:46+00:00

When configuring the broadcast timer on entry to and exit from deep idle
states, prefer a per-CPU wakeup timer if one exists.

On entry to idle, stop the tick device and transfer the next event into
the oneshot wakeup device, which will serve as the wakeup from idle. To
avoid the overhead of additional hardware accesses on exit from idle,
leave the timer armed and treat the inevitable interrupt as a (possibly
spurious) tick event.

Signed-off-by: Will Deacon 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210524221818.15850-5-will@kernel.org

tick/broadcast: Prefer per-cpu oneshot wakeup timers to broadcast

2021-05-31T15:04:45+00:00

Some SoCs have two per-cpu timer implementations where the timer with the
higher rating stops in deep idle (i.e. suffers from CLOCK_EVT_FEAT_C3STOP)
but is otherwise preferable to the timer with the lower rating. In such a
design, selecting the higher rated devices relies on a global broadcast
timer and IPIs to wake up from deep idle states.

To avoid the reliance on a global broadcast timer and also to reduce the
overhead associated with the IPI wakeups, extend
tick_install_broadcast_device() to manage per-cpu wakeup timers separately
from the broadcast device.

For now, these timers remain unused.

Signed-off-by: Will Deacon 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210524221818.15850-4-will@kernel.org

tick/broadcast: Split __tick_broadcast_oneshot_control() into a helper

2021-05-31T15:04:45+00:00

In preparation for adding support for per-cpu wakeup timers, split
_tick_broadcast_oneshot_control() into a helper function which deals
only with the broadcast timer management across idle transitions.

Signed-off-by: Will Deacon 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210524221818.15850-3-will@kernel.org

tick/broadcast: Drop unneeded CONFIG_GENERIC_CLOCKEVENTS_BROADCAST guard

2021-05-31T15:04:44+00:00

tick-broadcast.o is only built if CONFIG_GENERIC_CLOCKEVENTS_BROADCAST=y
so remove the redundant #ifdef guards around the definition of
tick_receive_broadcast().

Signed-off-by: Will Deacon 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210524221818.15850-2-will@kernel.org

tick/broadcast: Allow late registered device to enter oneshot mode

2021-04-16T19:03:50+00:00

The broadcast device is switched to oneshot mode when the system switches
to oneshot mode. If a broadcast clock event device is registered after the
system switched to oneshot mode, it will stay in periodic mode forever.

Ensure that a late registered device which is selected as broadcast device
is initialized in oneshot mode when the system already uses oneshot mode.

[ tglx: Massage changelog ]

Signed-off-by: Jindong Yue 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20210331083318.21794-1-jindong.yue@nxp.com

timekeeping, clocksource: Fix various typos in comments

2021-03-22T22:06:48+00:00

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

Signed-off-by: Ingo Molnar 
Cc: Thomas Gleixner 
Cc: John Stultz 
Cc: Stephen Boyd 
Cc: Daniel Lezcano 
Cc: linux-kernel@vger.kernel.org

tick: Get rid of tick_period

2020-11-19T09:48:29+00:00

The variable tick_period is initialized to NSEC_PER_TICK / HZ during boot
and never updated again.

If NSEC_PER_TICK is not an integer multiple of HZ this computation is less
accurate than TICK_NSEC which has proper rounding in place.

Aside of the inaccuracy there is no reason for having this variable at
all. It's just a pointless indirection and all usage sites can just use the
TICK_NSEC constant.

Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20201117132006.766643526@linutronix.de

tick/broadcast: Serialize access to tick_next_period

2020-11-19T09:48:28+00:00

tick_broadcast_setup_oneshot() accesses tick_next_period twice without any
serialization. This is wrong in two aspects:

  - Reading it twice might make the broadcast data inconsistent if the
    variable is updated concurrently.

  - On 32bit systems the access might see an partial update

Protect it with jiffies_lock. That's safe as none of the callchains leading
up to this function can create a lock ordering violation:

timer interrupt
  run_local_timers()
    hrtimer_run_queues()
      hrtimer_switch_to_hres()
        tick_init_highres()
	  tick_switch_to_oneshot()
	    tick_broadcast_switch_to_oneshot()
or
     tick_check_oneshot_change()
       tick_nohz_switch_to_nohz()
         tick_switch_to_oneshot()
           tick_broadcast_switch_to_oneshot()

Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20201117132006.061341507@linutronix.de

treewide: Use fallthrough pseudo-keyword

2020-08-23T22:36:59+00:00

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through markings when it is the case.

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through

Signed-off-by: Gustavo A. R. Silva