timekeeping: Make the MONOTONIC clock behave like the BOOTTIME clock
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>
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@ -419,6 +419,19 @@ void tick_suspend_local(void)
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clockevents_shutdown(td->evtdev);
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}
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static void tick_forward_next_period(void)
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{
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ktime_t delta, now = ktime_get();
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u64 n;
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delta = ktime_sub(now, tick_next_period);
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n = ktime_divns(delta, tick_period);
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tick_next_period += n * tick_period;
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if (tick_next_period < now)
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tick_next_period += tick_period;
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tick_sched_forward_next_period();
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}
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/**
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* tick_resume_local - Resume the local tick device
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*
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@ -431,6 +444,8 @@ void tick_resume_local(void)
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struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
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bool broadcast = tick_resume_check_broadcast();
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tick_forward_next_period();
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clockevents_tick_resume(td->evtdev);
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if (!broadcast) {
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if (td->mode == TICKDEV_MODE_PERIODIC)
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@ -141,6 +141,12 @@ 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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@ -51,6 +51,15 @@ struct tick_sched *tick_get_tick_sched(int cpu)
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*/
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static ktime_t last_jiffies_update;
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/*
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* Called after resume. Make sure that jiffies are not fast forwarded due to
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* clock monotonic being forwarded by the suspended time.
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*/
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void tick_sched_forward_next_period(void)
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{
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last_jiffies_update = tick_next_period;
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}
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/*
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* Must be called with interrupts disabled !
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*/
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@ -138,7 +138,9 @@ static void tk_set_wall_to_mono(struct timekeeper *tk, struct timespec64 wtm)
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static inline void tk_update_sleep_time(struct timekeeper *tk, ktime_t delta)
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{
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tk->offs_boot = ktime_add(tk->offs_boot, delta);
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/* Update both bases so mono and raw stay coupled. */
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tk->tkr_mono.base += delta;
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tk->tkr_raw.base += delta;
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/* Accumulate time spent in suspend */
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tk->time_suspended += delta;
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@ -1622,7 +1624,6 @@ static void __timekeeping_inject_sleeptime(struct timekeeper *tk,
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return;
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}
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tk_xtime_add(tk, delta);
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tk_set_wall_to_mono(tk, timespec64_sub(tk->wall_to_monotonic, *delta));
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tk_update_sleep_time(tk, timespec64_to_ktime(*delta));
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tk_debug_account_sleep_time(delta);
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}
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@ -2155,7 +2156,7 @@ out:
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void getboottime64(struct timespec64 *ts)
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{
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struct timekeeper *tk = &tk_core.timekeeper;
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ktime_t t = ktime_sub(tk->offs_real, tk->offs_boot);
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ktime_t t = ktime_sub(tk->offs_real, tk->time_suspended);
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*ts = ktime_to_timespec64(t);
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}
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