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Message-ID: <173696726061.31546.10518774114228471040.tip-bot2@tip-bot2>
Date: Wed, 15 Jan 2025 18:54:20 -0000
From: "tip-bot2 for Dr. David Alan Gilbert" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Dr. David Alan Gilbert" <linux@...blig.org>,
Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject:
[tip: timers/core] timekeeping: Remove unused ktime_get_fast_timestamps()
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@...blig.org>
AuthorDate: Sun, 12 Jan 2025 16:01:32
Committer: Thomas Gleixner <tglx@...utronix.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@...blig.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.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.
*
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