[PATCH] timekeeping: Remove unused ktime_get_fast_timestamps

[PATCH] timekeeping: Remove unused ktime_get_fast_timestamps

[linux]

From: "Dr. David Alan Gilbert" <linux@treblig.org>

ktime_get_fast_timestamps() was added in 2020 by
commit e2d977c9f1ab ("timekeeping: Provide multi-timestamp accessor to
NMI safe timekeeper")

but has remained unused.

Remove it.

(Perhaps it's worth just reverting the entire commit, the only bit
left is the extra parameter on __ktime_get_real_fast which is now
always NULL).

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
---
 include/linux/timekeeping.h | 15 -----------
 kernel/time/timekeeping.c   | 54 -------------------------------------
 2 files changed, 69 deletions(-)

diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 0e035f675efe..542773650200 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -263,18 +263,6 @@ extern bool timekeeping_rtc_skipresume(void);
 
 extern void timekeeping_inject_sleeptime64(const struct timespec64 *delta);
 
-/**
- * struct ktime_timestamps - Simultaneous mono/boot/real timestamps
- * @mono:	Monotonic timestamp
- * @boot:	Boottime timestamp
- * @real:	Realtime timestamp
- */
-struct ktime_timestamps {
-	u64		mono;
-	u64		boot;
-	u64		real;
-};
-
 /**
  * struct system_time_snapshot - simultaneous raw/real time capture with
  *				 counter value
@@ -345,9 +333,6 @@ extern int get_device_system_crosststamp(
  */
 extern void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot);
 
-/* NMI safe mono/boot/realtime timestamps */
-extern void ktime_get_fast_timestamps(struct ktime_timestamps *snap);
-
 /*
  * Persistent clock related interfaces
  */
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 3d128825d343..2f9de089bc0d 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -515,60 +515,6 @@ u64 ktime_get_real_fast_ns(void)
 }
 EXPORT_SYMBOL_GPL(ktime_get_real_fast_ns);
 
-/**
- * ktime_get_fast_timestamps: - NMI safe timestamps
- * @snapshot:	Pointer to timestamp storage
- *
- * Stores clock monotonic, boottime and realtime timestamps.
- *
- * Boot time is a racy access on 32bit systems if the sleep time injection
- * happens late during resume and not in timekeeping_resume(). That could
- * be avoided by expanding struct tk_read_base with boot offset for 32bit
- * and adding more overhead to the update. As this is a hard to observe
- * once per resume event which can be filtered with reasonable effort using
- * the accurate mono/real timestamps, it's probably not worth the trouble.
- *
- * Aside of that it might be possible on 32 and 64 bit to observe the
- * following when the sleep time injection happens late:
- *
- * CPU 0				CPU 1
- * timekeeping_resume()
- * ktime_get_fast_timestamps()
- *	mono, real = __ktime_get_real_fast()
- *					inject_sleep_time()
- *					   update boot offset
- *	boot = mono + bootoffset;
- *
- * That means that boot time already has the sleep time adjustment, but
- * real time does not. On the next readout both are in sync again.
- *
- * Preventing this for 64bit is not really feasible without destroying the
- * careful cache layout of the timekeeper because the sequence count and
- * struct tk_read_base would then need two cache lines instead of one.
- *
- * Access to the time keeper clock source is disabled across the innermost
- * steps of suspend/resume. The accessors still work, but the timestamps
- * are frozen until time keeping is resumed which happens very early.
- *
- * For regular suspend/resume there is no observable difference vs. sched
- * clock, but it might affect some of the nasty low level debug printks.
- *
- * OTOH, access to sched clock is not guaranteed across suspend/resume on
- * all systems either so it depends on the hardware in use.
- *
- * If that turns out to be a real problem then this could be mitigated by
- * using sched clock in a similar way as during early boot. But it's not as
- * trivial as on early boot because it needs some careful protection
- * against the clock monotonic timestamp jumping backwards on resume.
- */
-void ktime_get_fast_timestamps(struct ktime_timestamps *snapshot)
-{
-	struct timekeeper *tk = &tk_core.timekeeper;
-
-	snapshot->real = __ktime_get_real_fast(&tk_fast_mono, &snapshot->mono);
-	snapshot->boot = snapshot->mono + ktime_to_ns(data_race(tk->offs_boot));
-}
-
 /**
  * halt_fast_timekeeper - Prevent fast timekeeper from accessing clocksource.
  * @tk: Timekeeper to snapshot.
-- 
2.47.1

[tip: timers/core] timekeeping: Remove unused ktime_get_fast_timestamps()

[tip-bot2 for Dr. David Alan Gilbert]

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     2d2a46cf23788a19e5450c6f9c86ab17f596c708
Gitweb:        https://git.kernel.org/tip/2d2a46cf23788a19e5450c6f9c86ab17f596c708
Author:        Dr. David Alan Gilbert <linux@treblig.org>
AuthorDate:    Sun, 12 Jan 2025 16:01:32 
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 15 Jan 2025 19:49:14 +01:00

timekeeping: Remove unused ktime_get_fast_timestamps()

ktime_get_fast_timestamps() was added in 2020 by commit e2d977c9f1ab
("timekeeping: Provide multi-timestamp accessor to NMI safe timekeeper")
but has remained unused.

Remove it.

[ tglx: Fold the inline as David suggested in the submission ]

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250112160132.450209-1-linux@treblig.org

---
 include/linux/timekeeping.h | 15 +-------
 kernel/time/timekeeping.c   | 77 +++---------------------------------
 2 files changed, 8 insertions(+), 84 deletions(-)

diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 0e035f6..5427736 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -264,18 +264,6 @@ extern bool timekeeping_rtc_skipresume(void);
 extern void timekeeping_inject_sleeptime64(const struct timespec64 *delta);
 
 /**
- * struct ktime_timestamps - Simultaneous mono/boot/real timestamps
- * @mono:	Monotonic timestamp
- * @boot:	Boottime timestamp
- * @real:	Realtime timestamp
- */
-struct ktime_timestamps {
-	u64		mono;
-	u64		boot;
-	u64		real;
-};
-
-/**
  * struct system_time_snapshot - simultaneous raw/real time capture with
  *				 counter value
  * @cycles:	Clocksource counter value to produce the system times
@@ -345,9 +333,6 @@ extern int get_device_system_crosststamp(
  */
 extern void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot);
 
-/* NMI safe mono/boot/realtime timestamps */
-extern void ktime_get_fast_timestamps(struct ktime_timestamps *snap);
-
 /*
  * Persistent clock related interfaces
  */
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 3d12882..1e67d07 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -485,91 +485,30 @@ u64 notrace ktime_get_tai_fast_ns(void)
 }
 EXPORT_SYMBOL_GPL(ktime_get_tai_fast_ns);
 
-static __always_inline u64 __ktime_get_real_fast(struct tk_fast *tkf, u64 *mono)
+/**
+ * ktime_get_real_fast_ns: - NMI safe and fast access to clock realtime.
+ *
+ * See ktime_get_mono_fast_ns() for documentation of the time stamp ordering.
+ */
+u64 ktime_get_real_fast_ns(void)
 {
+	struct tk_fast *tkf = &tk_fast_mono;
 	struct tk_read_base *tkr;
-	u64 basem, baser, delta;
+	u64 baser, delta;
 	unsigned int seq;
 
 	do {
 		seq = raw_read_seqcount_latch(&tkf->seq);
 		tkr = tkf->base + (seq & 0x01);
-		basem = ktime_to_ns(tkr->base);
 		baser = ktime_to_ns(tkr->base_real);
 		delta = timekeeping_get_ns(tkr);
 	} while (raw_read_seqcount_latch_retry(&tkf->seq, seq));
 
-	if (mono)
-		*mono = basem + delta;
 	return baser + delta;
 }
-
-/**
- * ktime_get_real_fast_ns: - NMI safe and fast access to clock realtime.
- *
- * See ktime_get_mono_fast_ns() for documentation of the time stamp ordering.
- */
-u64 ktime_get_real_fast_ns(void)
-{
-	return __ktime_get_real_fast(&tk_fast_mono, NULL);
-}
 EXPORT_SYMBOL_GPL(ktime_get_real_fast_ns);
 
 /**
- * ktime_get_fast_timestamps: - NMI safe timestamps
- * @snapshot:	Pointer to timestamp storage
- *
- * Stores clock monotonic, boottime and realtime timestamps.
- *
- * Boot time is a racy access on 32bit systems if the sleep time injection
- * happens late during resume and not in timekeeping_resume(). That could
- * be avoided by expanding struct tk_read_base with boot offset for 32bit
- * and adding more overhead to the update. As this is a hard to observe
- * once per resume event which can be filtered with reasonable effort using
- * the accurate mono/real timestamps, it's probably not worth the trouble.
- *
- * Aside of that it might be possible on 32 and 64 bit to observe the
- * following when the sleep time injection happens late:
- *
- * CPU 0				CPU 1
- * timekeeping_resume()
- * ktime_get_fast_timestamps()
- *	mono, real = __ktime_get_real_fast()
- *					inject_sleep_time()
- *					   update boot offset
- *	boot = mono + bootoffset;
- *
- * That means that boot time already has the sleep time adjustment, but
- * real time does not. On the next readout both are in sync again.
- *
- * Preventing this for 64bit is not really feasible without destroying the
- * careful cache layout of the timekeeper because the sequence count and
- * struct tk_read_base would then need two cache lines instead of one.
- *
- * Access to the time keeper clock source is disabled across the innermost
- * steps of suspend/resume. The accessors still work, but the timestamps
- * are frozen until time keeping is resumed which happens very early.
- *
- * For regular suspend/resume there is no observable difference vs. sched
- * clock, but it might affect some of the nasty low level debug printks.
- *
- * OTOH, access to sched clock is not guaranteed across suspend/resume on
- * all systems either so it depends on the hardware in use.
- *
- * If that turns out to be a real problem then this could be mitigated by
- * using sched clock in a similar way as during early boot. But it's not as
- * trivial as on early boot because it needs some careful protection
- * against the clock monotonic timestamp jumping backwards on resume.
- */
-void ktime_get_fast_timestamps(struct ktime_timestamps *snapshot)
-{
-	struct timekeeper *tk = &tk_core.timekeeper;
-
-	snapshot->real = __ktime_get_real_fast(&tk_fast_mono, &snapshot->mono);
-	snapshot->boot = snapshot->mono + ktime_to_ns(data_race(tk->offs_boot));
-}
-
-/**
  * halt_fast_timekeeper - Prevent fast timekeeper from accessing clocksource.
  * @tk: Timekeeper to snapshot.
  *