4396e058c5
Tracers want a correlated time between the kernel instrumentation and
user space. We really do not want to export sched_clock() to user
space, so we need to provide something sensible for this.
Using separate data structures with an non blocking sequence count
based update mechanism allows us to do that. The data structure
required for the readout has a sequence counter and two copies of the
timekeeping data.
On the update side:
smp_wmb();
tkf->seq++;
smp_wmb();
update(tkf->base[0], tk);
smp_wmb();
tkf->seq++;
smp_wmb();
update(tkf->base[1], tk);
On the reader side:
do {
seq = tkf->seq;
smp_rmb();
idx = seq & 0x01;
now = now(tkf->base[idx]);
smp_rmb();
} while (seq != tkf->seq)
So if a NMI hits the update of base[0] it will use base[1] which is
still consistent, but this timestamp is not guaranteed to be monotonic
across an update.
The timestamp is calculated by:
now = base_mono + clock_delta * slope
So if the update lowers the slope, readers who are forced to the
not yet updated second array are still using the old steeper slope.
tmono
^
| o n
| o n
| u
| o
|o
|12345678---> reader order
o = old slope
u = update
n = new slope
So reader 6 will observe time going backwards versus reader 5.
While other CPUs are likely to be able observe that, the only way
for a CPU local observation is when an NMI hits in the middle of
the update. Timestamps taken from that NMI context might be ahead
of the following timestamps. Callers need to be aware of that and
deal with it.
V2: Got rid of clock monotonic raw and reorganized the data
structures. Folded in the barrier fix from Mathieu.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
209 lines
4.3 KiB
C
209 lines
4.3 KiB
C
#ifndef _LINUX_TIMEKEEPING_H
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#define _LINUX_TIMEKEEPING_H
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/* Included from linux/ktime.h */
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void timekeeping_init(void);
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extern int timekeeping_suspended;
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/*
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* Get and set timeofday
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*/
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extern void do_gettimeofday(struct timeval *tv);
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extern int do_settimeofday(const struct timespec *tv);
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extern int do_sys_settimeofday(const struct timespec *tv,
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const struct timezone *tz);
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/*
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* Kernel time accessors
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*/
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unsigned long get_seconds(void);
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struct timespec current_kernel_time(void);
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/* does not take xtime_lock */
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struct timespec __current_kernel_time(void);
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/*
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* timespec based interfaces
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*/
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struct timespec get_monotonic_coarse(void);
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extern void getrawmonotonic(struct timespec *ts);
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extern void ktime_get_ts64(struct timespec64 *ts);
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extern int __getnstimeofday64(struct timespec64 *tv);
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extern void getnstimeofday64(struct timespec64 *tv);
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#if BITS_PER_LONG == 64
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static inline int __getnstimeofday(struct timespec *ts)
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{
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return __getnstimeofday64(ts);
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}
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static inline void getnstimeofday(struct timespec *ts)
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{
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getnstimeofday64(ts);
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}
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static inline void ktime_get_ts(struct timespec *ts)
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{
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ktime_get_ts64(ts);
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}
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static inline void ktime_get_real_ts(struct timespec *ts)
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{
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getnstimeofday64(ts);
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}
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#else
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static inline int __getnstimeofday(struct timespec *ts)
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{
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struct timespec64 ts64;
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int ret = __getnstimeofday64(&ts64);
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*ts = timespec64_to_timespec(ts64);
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return ret;
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}
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static inline void getnstimeofday(struct timespec *ts)
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{
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struct timespec64 ts64;
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getnstimeofday64(&ts64);
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*ts = timespec64_to_timespec(ts64);
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}
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static inline void ktime_get_ts(struct timespec *ts)
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{
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struct timespec64 ts64;
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ktime_get_ts64(&ts64);
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*ts = timespec64_to_timespec(ts64);
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}
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static inline void ktime_get_real_ts(struct timespec *ts)
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{
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struct timespec64 ts64;
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getnstimeofday64(&ts64);
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*ts = timespec64_to_timespec(ts64);
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}
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#endif
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extern void getboottime(struct timespec *ts);
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#define do_posix_clock_monotonic_gettime(ts) ktime_get_ts(ts)
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#define ktime_get_real_ts64(ts) getnstimeofday64(ts)
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/*
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* ktime_t based interfaces
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*/
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enum tk_offsets {
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TK_OFFS_REAL,
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TK_OFFS_BOOT,
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TK_OFFS_TAI,
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TK_OFFS_MAX,
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};
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extern ktime_t ktime_get(void);
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extern ktime_t ktime_get_with_offset(enum tk_offsets offs);
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extern ktime_t ktime_mono_to_any(ktime_t tmono, enum tk_offsets offs);
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extern ktime_t ktime_get_raw(void);
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/**
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* ktime_get_real - get the real (wall-) time in ktime_t format
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*/
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static inline ktime_t ktime_get_real(void)
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{
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return ktime_get_with_offset(TK_OFFS_REAL);
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}
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/**
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* ktime_get_boottime - Returns monotonic time since boot in ktime_t format
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*
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* This is similar to CLOCK_MONTONIC/ktime_get, but also includes the
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* time spent in suspend.
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*/
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static inline ktime_t ktime_get_boottime(void)
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{
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return ktime_get_with_offset(TK_OFFS_BOOT);
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}
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/**
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* ktime_get_clocktai - Returns the TAI time of day in ktime_t format
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*/
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static inline ktime_t ktime_get_clocktai(void)
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{
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return ktime_get_with_offset(TK_OFFS_TAI);
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}
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/**
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* ktime_mono_to_real - Convert monotonic time to clock realtime
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*/
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static inline ktime_t ktime_mono_to_real(ktime_t mono)
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{
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return ktime_mono_to_any(mono, TK_OFFS_REAL);
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}
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static inline u64 ktime_get_ns(void)
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{
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return ktime_to_ns(ktime_get());
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}
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static inline u64 ktime_get_real_ns(void)
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{
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return ktime_to_ns(ktime_get_real());
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}
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static inline u64 ktime_get_boot_ns(void)
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{
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return ktime_to_ns(ktime_get_boottime());
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}
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static inline u64 ktime_get_raw_ns(void)
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{
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return ktime_to_ns(ktime_get_raw());
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}
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extern u64 ktime_get_mono_fast_ns(void);
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/*
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* Timespec interfaces utilizing the ktime based ones
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*/
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static inline void get_monotonic_boottime(struct timespec *ts)
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{
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*ts = ktime_to_timespec(ktime_get_boottime());
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}
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static inline void timekeeping_clocktai(struct timespec *ts)
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{
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*ts = ktime_to_timespec(ktime_get_clocktai());
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}
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/*
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* RTC specific
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*/
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extern void timekeeping_inject_sleeptime(struct timespec *delta);
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/*
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* PPS accessor
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*/
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extern void getnstime_raw_and_real(struct timespec *ts_raw,
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struct timespec *ts_real);
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/*
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* Persistent clock related interfaces
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*/
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extern bool persistent_clock_exist;
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extern int persistent_clock_is_local;
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static inline bool has_persistent_clock(void)
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{
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return persistent_clock_exist;
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}
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extern void read_persistent_clock(struct timespec *ts);
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extern void read_boot_clock(struct timespec *ts);
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extern int update_persistent_clock(struct timespec now);
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#endif
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