timekeeping: Implement a shadow timekeeper
Use the shadow timekeeper to do the update_wall_time() adjustments and then copy it over to the real timekeeper. Keep the shadow timekeeper in sync when updating stuff outside of update_wall_time(). This allows us to limit the timekeeper_seq hold time to the update of the real timekeeper and the vsyscall data in the next patch. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: John Stultz <john.stultz@linaro.org>
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@ -29,6 +29,7 @@
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static struct timekeeper timekeeper;
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static DEFINE_RAW_SPINLOCK(timekeeper_lock);
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static seqcount_t timekeeper_seq;
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static struct timekeeper shadow_timekeeper;
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/* flag for if timekeeping is suspended */
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int __read_mostly timekeeping_suspended;
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@ -240,7 +241,7 @@ int pvclock_gtod_unregister_notifier(struct notifier_block *nb)
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EXPORT_SYMBOL_GPL(pvclock_gtod_unregister_notifier);
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/* must hold timekeeper_lock */
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static void timekeeping_update(struct timekeeper *tk, bool clearntp)
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static void timekeeping_update(struct timekeeper *tk, bool clearntp, bool mirror)
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{
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if (clearntp) {
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tk->ntp_error = 0;
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@ -248,6 +249,9 @@ static void timekeeping_update(struct timekeeper *tk, bool clearntp)
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}
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update_vsyscall(tk);
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update_pvclock_gtod(tk);
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if (mirror)
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memcpy(&shadow_timekeeper, &timekeeper, sizeof(timekeeper));
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}
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/**
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@ -504,7 +508,7 @@ int do_settimeofday(const struct timespec *tv)
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tk_set_xtime(tk, tv);
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timekeeping_update(tk, true);
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timekeeping_update(tk, true, true);
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write_seqcount_end(&timekeeper_seq);
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raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
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@ -548,7 +552,7 @@ int timekeeping_inject_offset(struct timespec *ts)
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tk_set_wall_to_mono(tk, timespec_sub(tk->wall_to_monotonic, *ts));
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error: /* even if we error out, we forwarded the time, so call update */
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timekeeping_update(tk, true);
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timekeeping_update(tk, true, true);
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write_seqcount_end(&timekeeper_seq);
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raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
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@ -628,7 +632,7 @@ static int change_clocksource(void *data)
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if (old->disable)
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old->disable(old);
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}
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timekeeping_update(tk, true);
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timekeeping_update(tk, true, true);
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write_seqcount_end(&timekeeper_seq);
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raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
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@ -809,6 +813,8 @@ void __init timekeeping_init(void)
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tmp.tv_nsec = 0;
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tk_set_sleep_time(tk, tmp);
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memcpy(&shadow_timekeeper, &timekeeper, sizeof(timekeeper));
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write_seqcount_end(&timekeeper_seq);
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raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
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}
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@ -865,7 +871,7 @@ void timekeeping_inject_sleeptime(struct timespec *delta)
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__timekeeping_inject_sleeptime(tk, delta);
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timekeeping_update(tk, true);
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timekeeping_update(tk, true, true);
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write_seqcount_end(&timekeeper_seq);
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raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
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@ -947,7 +953,7 @@ static void timekeeping_resume(void)
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clock->cycle_last = cycle_now;
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tk->ntp_error = 0;
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timekeeping_suspended = 0;
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timekeeping_update(tk, false);
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timekeeping_update(tk, false, true);
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write_seqcount_end(&timekeeper_seq);
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raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
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@ -1328,7 +1334,8 @@ static inline void old_vsyscall_fixup(struct timekeeper *tk)
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static void update_wall_time(void)
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{
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struct clocksource *clock;
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struct timekeeper *tk = &timekeeper;
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struct timekeeper *real_tk = &timekeeper;
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struct timekeeper *tk = &shadow_timekeeper;
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cycle_t offset;
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int shift = 0, maxshift;
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unsigned long flags;
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@ -1340,16 +1347,16 @@ static void update_wall_time(void)
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if (unlikely(timekeeping_suspended))
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goto out;
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clock = tk->clock;
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clock = real_tk->clock;
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#ifdef CONFIG_ARCH_USES_GETTIMEOFFSET
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offset = tk->cycle_interval;
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offset = real_tk->cycle_interval;
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#else
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offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
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#endif
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/* Check if there's really nothing to do */
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if (offset < tk->cycle_interval)
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if (offset < real_tk->cycle_interval)
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goto out;
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/*
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@ -1388,12 +1395,22 @@ static void update_wall_time(void)
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/* Update clock->cycle_last with the new value */
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clock->cycle_last = tk->cycle_last;
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timekeeping_update(tk, false);
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/*
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* Update the real timekeeper.
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*
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* We could avoid this memcpy by switching pointers, but that
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* requires changes to all other timekeeper usage sites as
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* well, i.e. move the timekeeper pointer getter into the
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* spinlocked/seqcount protected sections. And we trade this
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* memcpy under the timekeeper_seq against one before we start
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* updating.
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*/
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memcpy(real_tk, tk, sizeof(*tk));
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timekeeping_update(real_tk, false, false);
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out:
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write_seqcount_end(&timekeeper_seq);
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raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
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}
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/**
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