[RFC v7 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 
---
 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(_lock, flags);
+   list_for_each_entry(dev, _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(_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);
 }
 
 /*
-- 
2.10.0

[RFC v7 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 
---
 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(_lock, flags);
+   list_for_each_entry(dev, _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(_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);
 }
 
 /*
-- 
2.10.0