Merge tag 'timers-core-2022-05-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer and timekeeping updates from Thomas Gleixner:

 - Expose CLOCK_TAI to instrumentation to aid with TSN debugging.

 - Ensure that the clockevent is stopped when there is no timer armed to
   avoid pointless wakeups.

 - Make the sched clock frequency handling and rounding consistent.

 - Provide a better debugobject hint for delayed works. The timer
   callback is always the same, which makes it difficult to identify the
   underlying work. Use the work function as a hint instead.

 - Move the timer specific sysctl code into the timer subsystem.

 - The usual set of improvements and cleanups

* tag 'timers-core-2022-05-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  timers: Provide a better debugobjects hint for delayed works
  time/sched_clock: Fix formatting of frequency reporting code
  time/sched_clock: Use Hz as the unit for clock rate reporting below 4kHz
  time/sched_clock: Round the frequency reported to nearest rather than down
  timekeeping: Consolidate fast timekeeper
  timekeeping: Annotate ktime_get_boot_fast_ns() with data_race()
  timers/nohz: Switch to ONESHOT_STOPPED in the low-res handler when the tick is stopped
  timekeeping: Introduce fast accessor to clock tai
  tracing/timer: Add missing argument documentation of trace points
  clocksource: Replace cpumask_weight() with cpumask_empty()
  timers: Move timer sysctl into the timer code
  clockevents: Use dedicated list iterator variable
  timers: Simplify calc_index()
  timers: Initialize base::next_expiry_recalc in timers_prepare_cpu()

1 files changed, 28 insertions, 11 deletions

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 3b1398fbddaf..4ab9949772d5 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -429,6 +429,14 @@ static void update_fast_timekeeper(const struct tk_read_base *tkr,
 	memcpy(base + 1, base, sizeof(*base));
 }
 
+static __always_inline u64 fast_tk_get_delta_ns(struct tk_read_base *tkr)
+{
+	u64 delta, cycles = tk_clock_read(tkr);
+
+	delta = clocksource_delta(cycles, tkr->cycle_last, tkr->mask);
+	return timekeeping_delta_to_ns(tkr, delta);
+}
+
 static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf)
 {
 	struct tk_read_base *tkr;
@@ -439,12 +447,7 @@ static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf)
 		seq = raw_read_seqcount_latch(&tkf->seq);
 		tkr = tkf->base + (seq & 0x01);
 		now = ktime_to_ns(tkr->base);
-
-		now += timekeeping_delta_to_ns(tkr,
-				clocksource_delta(
-					tk_clock_read(tkr),
-					tkr->cycle_last,
-					tkr->mask));
+		now += fast_tk_get_delta_ns(tkr);
 	} while (read_seqcount_latch_retry(&tkf->seq, seq));
 
 	return now;
@@ -528,10 +531,27 @@ u64 notrace ktime_get_boot_fast_ns(void)
 {
 	struct timekeeper *tk = &tk_core.timekeeper;
 
-	return (ktime_get_mono_fast_ns() + ktime_to_ns(tk->offs_boot));
+	return (ktime_get_mono_fast_ns() + ktime_to_ns(data_race(tk->offs_boot)));
 }
 EXPORT_SYMBOL_GPL(ktime_get_boot_fast_ns);
 
+/**
+ * ktime_get_tai_fast_ns - NMI safe and fast access to tai clock.
+ *
+ * The same limitations as described for ktime_get_boot_fast_ns() apply. The
+ * mono time and the TAI offset are not read atomically which may yield wrong
+ * readouts. However, an update of the TAI offset is an rare event e.g., caused
+ * by settime or adjtimex with an offset. The user of this function has to deal
+ * with the possibility of wrong timestamps in post processing.
+ */
+u64 notrace ktime_get_tai_fast_ns(void)
+{
+	struct timekeeper *tk = &tk_core.timekeeper;
+
+	return (ktime_get_mono_fast_ns() + ktime_to_ns(data_race(tk->offs_tai)));
+}
+EXPORT_SYMBOL_GPL(ktime_get_tai_fast_ns);
+
 static __always_inline u64 __ktime_get_real_fast(struct tk_fast *tkf, u64 *mono)
 {
 	struct tk_read_base *tkr;
@@ -543,10 +563,7 @@ static __always_inline u64 __ktime_get_real_fast(struct tk_fast *tkf, u64 *mono)
 		tkr = tkf->base + (seq & 0x01);
 		basem = ktime_to_ns(tkr->base);
 		baser = ktime_to_ns(tkr->base_real);
-
-		delta = timekeeping_delta_to_ns(tkr,
-				clocksource_delta(tk_clock_read(tkr),
-				tkr->cycle_last, tkr->mask));
+		delta = fast_tk_get_delta_ns(tkr);
 	} while (read_seqcount_latch_retry(&tkf->seq, seq));
 
 	if (mono)