From 2d2a46cf23788a19e5450c6f9c86ab17f596c708 Mon Sep 17 00:00:00 2001 From: "Dr. David Alan Gilbert" Date: Sun, 12 Jan 2025 16:01:32 +0000 Subject: [PATCH] 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 Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/all/20250112160132.450209-1-linux@treblig.org --- include/linux/timekeeping.h | 15 ------- kernel/time/timekeeping.c | 87 ++++++------------------------------- 2 files changed, 13 insertions(+), 89 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..1e67d076f195 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -485,25 +485,6 @@ 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) -{ - struct tk_read_base *tkr; - u64 basem, 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. * @@ -511,64 +492,22 @@ static __always_inline u64 __ktime_get_real_fast(struct tk_fast *tkf, u64 *mono) */ u64 ktime_get_real_fast_ns(void) { - return __ktime_get_real_fast(&tk_fast_mono, NULL); + struct tk_fast *tkf = &tk_fast_mono; + struct tk_read_base *tkr; + u64 baser, delta; + unsigned int seq; + + do { + seq = raw_read_seqcount_latch(&tkf->seq); + tkr = tkf->base + (seq & 0x01); + baser = ktime_to_ns(tkr->base_real); + delta = timekeeping_get_ns(tkr); + } while (raw_read_seqcount_latch_retry(&tkf->seq, seq)); + + return baser + delta; } 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.