[RFC v6 23/23] timekeeping: inform clockevents about freq adjustments

[Nicolai Stange]

Upon adjustments of the monotonic clock's frequencies from the
timekeeping core, the clockevents devices' ->mult_adjusted should be
changed accordingly, too.

Introduce clockevents_adjust_all_freqs() which traverses all registered
clockevent devices and, if the CLOCK_EVT_FEAT_NO_ADJUST flag is not set,
recalculates their ->mult_adjusted based on the monotonic clock's current
frequency.

Call clockevents_adjust_all_freqs() from timekeeping_freqadjust().

Note that it might look like as if timekeeping_apply_adjustment() was the
more natural candidate to trigger the clockevent devices' frequency updates
from: it's the single place where the mono clock's ->mult is changed.
However, timekeeping_apply_adjustment() is also invoked for the
on-off-controlled adjustments made to the mono clock's ->mult from
timekeeping_adjust(). These adjustments are very small in magnitude and,
more importantly, exhibit some oscillatory behaviour once the NTP error
becomes small. We don't want the clockevent devices' ->mult values to
follow these oscillations because they're negligible and because the
process of updating them would periodically destroy what
clockevents_increase_min_delta() might have built up.

Signed-off-by: Nicolai Stange <nicstange@xxxxxxxxx>
---
 kernel/time/clockevents.c   | 33 +++++++++++++++++++++++++++++++++
 kernel/time/tick-internal.h |  5 +++++
 kernel/time/timekeeping.c   |  2 ++
 3 files changed, 40 insertions(+)

diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index b121932..e009add 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -626,6 +626,39 @@ void __clockevents_adjust_freq(struct clock_event_device *dev)
 							mult_cs_raw);
 }
 
+void clockevents_adjust_all_freqs(u32 mult_cs_mono, u32 mult_cs_raw)
+{
+	u32 last_mult_raw = 0, last_shift = 0, last_mult_adjusted = 0;
+	u32 mult_raw, shift;
+	unsigned long flags;
+	struct clock_event_device *dev;
+
+	raw_spin_lock_irqsave(&clockevents_lock, flags);
+	list_for_each_entry(dev, &clockevent_devices, list) {
+		if (!(dev->features & CLOCK_EVT_FEAT_ONESHOT) ||
+		     (dev->features & CLOCK_EVT_FEAT_NO_ADJUST))
+			continue;
+
+		/*
+		 * The cached last_mult_adjusted is only valid if
+		 * shift == last_shift. Otherwise, it could exceed
+		 * what is allowed by ->max_delta_ns.
+		 */
+		mult_raw = dev->mult;
+		shift = dev->shift;
+		if (mult_raw != last_mult_raw || shift != last_shift) {
+			last_mult_raw = mult_raw;
+			last_shift = shift;
+			last_mult_adjusted =
+				__clockevents_calc_adjust_freq(mult_raw,
+							mult_cs_mono,
+							mult_cs_raw);
+		}
+		dev->mult_adjusted = last_mult_adjusted;
+	}
+	raw_spin_unlock_irqrestore(&clockevents_lock, flags);
+}
+
 int __clockevents_update_freq(struct clock_event_device *dev, u32 freq)
 {
 	clockevents_config(dev, freq);
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 0b29d23..2d97c42 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -56,6 +56,7 @@ extern int clockevents_program_event(struct clock_event_device *dev,
 				     ktime_t expires, bool force);
 extern void clockevents_handle_noop(struct clock_event_device *dev);
 extern int __clockevents_update_freq(struct clock_event_device *dev, u32 freq);
+extern void clockevents_adjust_all_freqs(u32 mult_cs_mono, u32 mult_cs_raw);
 extern void timekeeping_get_mono_mult(u32 *mult_cs_mono, u32 *mult_cs_raw);
 extern ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt);
 
@@ -95,6 +96,10 @@ static inline void tick_set_periodic_handler(struct clock_event_device *dev, int
 #else /* !GENERIC_CLOCKEVENTS: */
 static inline void tick_suspend(void) { }
 static inline void tick_resume(void) { }
+
+static inline void clockevents_adjust_all_freqs(u32 mult_cs_mono,
+						u32 mult_cs_raw)
+{}
 #endif /* !GENERIC_CLOCKEVENTS */
 
 /* Oneshot related functions */
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 7ddca9e..f55926b 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1910,6 +1910,8 @@ static __always_inline void timekeeping_freqadjust(struct timekeeper *tk,
 
 	/* scale the corrections */
 	timekeeping_apply_adjustment(tk, offset, negative, adj_scale);
+	clockevents_adjust_all_freqs(tk->tkr_mono.mult,
+				tk->tkr_mono.clock->mult);
 }
 
 /*
-- 
2.9.3