![Thomas Gleixner](/assets/img/avatar_default.png)
The MONOTONIC clock is not fast forwarded by the time spent in suspend on resume. This is only done for the BOOTTIME clock. The reason why the MONOTONIC clock is not forwarded is historical: the original Linux implementation was using jiffies as a base for the MONOTONIC clock and jiffies have never been advanced after resume. At some point when timekeeping was unified in the core code, the MONONOTIC clock was advanced after resume which also advanced jiffies causing interesting side effects. As a consequence the the MONOTONIC clock forwarding was disabled again and the BOOTTIME clock was introduced, which allows to read time since boot. Back then it was not possible to completely distangle the MONOTONIC clock and jiffies because there were still interfaces which exposed the MONOTONIC clock behaviour based on the timer wheel and therefore jiffies. As of today none of the MONOTONIC clock facilities depends on jiffies anymore so the forwarding can be done seperately. This is achieved by forwarding the variables which are used for the jiffies update after resume before the tick is restarted, In timekeeping resume, the change is rather simple. Instead of updating the offset between the MONOTONIC clock and the REALTIME/BOOTTIME clocks, advance the time keeper base for the MONOTONIC and the MONOTONIC_RAW clocks by the time spent in suspend. The MONOTONIC clock is now the same as the BOOTTIME clock and the offset between the REALTIME and the MONOTONIC clocks is the same as before suspend. There might be side effects in applications, which rely on the (unfortunately) well documented behaviour of the MONOTONIC clock, but the downsides of the existing behaviour are probably worse. There is one obvious issue. Up to now it was possible to retrieve the time spent in suspend by observing the delta between the MONOTONIC clock and the BOOTTIME clock. This is not longer available, but the previously introduced mechanism to read the active non-suspended monotonic time can mitigate that in a detectable fashion. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com> Cc: John Stultz <john.stultz@linaro.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Kevin Easton <kevin@guarana.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mark Salyzyn <salyzyn@android.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Petr Mladek <pmladek@suse.com> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Link: http://lkml.kernel.org/r/20180301165150.062975504@linutronix.de Signed-off-by: Ingo Molnar <mingo@kernel.org>
172 lines
7.1 KiB
C
172 lines
7.1 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* tick internal variable and functions used by low/high res code
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*/
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#include <linux/hrtimer.h>
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#include <linux/tick.h>
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#include "timekeeping.h"
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#include "tick-sched.h"
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#ifdef CONFIG_GENERIC_CLOCKEVENTS
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# define TICK_DO_TIMER_NONE -1
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# define TICK_DO_TIMER_BOOT -2
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DECLARE_PER_CPU(struct tick_device, tick_cpu_device);
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extern ktime_t tick_next_period;
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extern ktime_t tick_period;
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extern int tick_do_timer_cpu __read_mostly;
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extern void tick_setup_periodic(struct clock_event_device *dev, int broadcast);
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extern void tick_handle_periodic(struct clock_event_device *dev);
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extern void tick_check_new_device(struct clock_event_device *dev);
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extern void tick_shutdown(unsigned int cpu);
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extern void tick_suspend(void);
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extern void tick_resume(void);
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extern bool tick_check_replacement(struct clock_event_device *curdev,
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struct clock_event_device *newdev);
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extern void tick_install_replacement(struct clock_event_device *dev);
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extern int tick_is_oneshot_available(void);
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extern struct tick_device *tick_get_device(int cpu);
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extern int clockevents_tick_resume(struct clock_event_device *dev);
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/* Check, if the device is functional or a dummy for broadcast */
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static inline int tick_device_is_functional(struct clock_event_device *dev)
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{
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return !(dev->features & CLOCK_EVT_FEAT_DUMMY);
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}
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static inline enum clock_event_state clockevent_get_state(struct clock_event_device *dev)
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{
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return dev->state_use_accessors;
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}
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static inline void clockevent_set_state(struct clock_event_device *dev,
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enum clock_event_state state)
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{
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dev->state_use_accessors = state;
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}
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extern void clockevents_shutdown(struct clock_event_device *dev);
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extern void clockevents_exchange_device(struct clock_event_device *old,
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struct clock_event_device *new);
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extern void clockevents_switch_state(struct clock_event_device *dev,
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enum clock_event_state state);
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extern int clockevents_program_event(struct clock_event_device *dev,
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ktime_t expires, bool force);
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extern void clockevents_handle_noop(struct clock_event_device *dev);
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extern int __clockevents_update_freq(struct clock_event_device *dev, u32 freq);
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extern ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt);
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/* Broadcasting support */
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# ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
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extern int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu);
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extern void tick_install_broadcast_device(struct clock_event_device *dev);
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extern int tick_is_broadcast_device(struct clock_event_device *dev);
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extern void tick_shutdown_broadcast(unsigned int cpu);
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extern void tick_suspend_broadcast(void);
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extern void tick_resume_broadcast(void);
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extern bool tick_resume_check_broadcast(void);
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extern void tick_broadcast_init(void);
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extern void tick_set_periodic_handler(struct clock_event_device *dev, int broadcast);
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extern int tick_broadcast_update_freq(struct clock_event_device *dev, u32 freq);
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extern struct tick_device *tick_get_broadcast_device(void);
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extern struct cpumask *tick_get_broadcast_mask(void);
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# else /* !CONFIG_GENERIC_CLOCKEVENTS_BROADCAST: */
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static inline void tick_install_broadcast_device(struct clock_event_device *dev) { }
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static inline int tick_is_broadcast_device(struct clock_event_device *dev) { return 0; }
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static inline int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu) { return 0; }
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static inline void tick_do_periodic_broadcast(struct clock_event_device *d) { }
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static inline void tick_shutdown_broadcast(unsigned int cpu) { }
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static inline void tick_suspend_broadcast(void) { }
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static inline void tick_resume_broadcast(void) { }
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static inline bool tick_resume_check_broadcast(void) { return false; }
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static inline void tick_broadcast_init(void) { }
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static inline int tick_broadcast_update_freq(struct clock_event_device *dev, u32 freq) { return -ENODEV; }
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/* Set the periodic handler in non broadcast mode */
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static inline void tick_set_periodic_handler(struct clock_event_device *dev, int broadcast)
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{
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dev->event_handler = tick_handle_periodic;
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}
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# endif /* !CONFIG_GENERIC_CLOCKEVENTS_BROADCAST */
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#else /* !GENERIC_CLOCKEVENTS: */
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static inline void tick_suspend(void) { }
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static inline void tick_resume(void) { }
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#endif /* !GENERIC_CLOCKEVENTS */
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/* Oneshot related functions */
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#ifdef CONFIG_TICK_ONESHOT
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extern void tick_setup_oneshot(struct clock_event_device *newdev,
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void (*handler)(struct clock_event_device *),
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ktime_t nextevt);
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extern int tick_program_event(ktime_t expires, int force);
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extern void tick_oneshot_notify(void);
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extern int tick_switch_to_oneshot(void (*handler)(struct clock_event_device *));
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extern void tick_resume_oneshot(void);
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static inline bool tick_oneshot_possible(void) { return true; }
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extern int tick_oneshot_mode_active(void);
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extern void tick_clock_notify(void);
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extern int tick_check_oneshot_change(int allow_nohz);
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extern int tick_init_highres(void);
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#else /* !CONFIG_TICK_ONESHOT: */
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static inline
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void tick_setup_oneshot(struct clock_event_device *newdev,
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void (*handler)(struct clock_event_device *),
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ktime_t nextevt) { BUG(); }
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static inline void tick_resume_oneshot(void) { BUG(); }
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static inline int tick_program_event(ktime_t expires, int force) { return 0; }
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static inline void tick_oneshot_notify(void) { }
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static inline bool tick_oneshot_possible(void) { return false; }
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static inline int tick_oneshot_mode_active(void) { return 0; }
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static inline void tick_clock_notify(void) { }
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static inline int tick_check_oneshot_change(int allow_nohz) { return 0; }
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#endif /* !CONFIG_TICK_ONESHOT */
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/* Functions related to oneshot broadcasting */
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#if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_TICK_ONESHOT)
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extern void tick_broadcast_switch_to_oneshot(void);
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extern void tick_shutdown_broadcast_oneshot(unsigned int cpu);
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extern int tick_broadcast_oneshot_active(void);
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extern void tick_check_oneshot_broadcast_this_cpu(void);
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bool tick_broadcast_oneshot_available(void);
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extern struct cpumask *tick_get_broadcast_oneshot_mask(void);
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#else /* !(BROADCAST && ONESHOT): */
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static inline void tick_broadcast_switch_to_oneshot(void) { }
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static inline void tick_shutdown_broadcast_oneshot(unsigned int cpu) { }
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static inline int tick_broadcast_oneshot_active(void) { return 0; }
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static inline void tick_check_oneshot_broadcast_this_cpu(void) { }
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static inline bool tick_broadcast_oneshot_available(void) { return tick_oneshot_possible(); }
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#endif /* !(BROADCAST && ONESHOT) */
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#if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
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extern void tick_sched_forward_next_period(void);
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#else
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static inline void tick_sched_forward_next_period(void) { }
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#endif
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/* NO_HZ_FULL internal */
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#ifdef CONFIG_NO_HZ_FULL
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extern void tick_nohz_init(void);
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# else
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static inline void tick_nohz_init(void) { }
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#endif
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#ifdef CONFIG_NO_HZ_COMMON
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extern unsigned long tick_nohz_active;
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extern void timers_update_nohz(void);
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# ifdef CONFIG_SMP
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extern struct static_key_false timers_migration_enabled;
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# endif
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#else /* CONFIG_NO_HZ_COMMON */
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static inline void timers_update_nohz(void) { }
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#define tick_nohz_active (0)
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#endif
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DECLARE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases);
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extern u64 get_next_timer_interrupt(unsigned long basej, u64 basem);
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void timer_clear_idle(void);
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