Commit 64123fd4 authored by Matt Helsley's avatar Matt Helsley Committed by Linus Torvalds

[PATCH] Add getnstimestamp function

There are several functions that might seem appropriate for a timestamp:

get_cycles()
current_kernel_time()
do_gettimeofday()
<read jiffies/jiffies_64>

Each has problems with combinations of SMP-safety, low resolution, and
monotonicity. This patch adds a new function that returns a monotonic SMP-safe
timestamp with nanosecond resolution where available.

Changes:
	Split timestamp into separate patch
	Moved to kernel/time.c
	Renamed to getnstimestamp
	Fixed unintended-pointer-arithmetic bug
Signed-off-by: default avatarMatt Helsley <matthltc@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 894ec870
......@@ -95,6 +95,7 @@ struct itimerval;
extern int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue);
extern int do_getitimer(int which, struct itimerval *value);
extern void getnstimeofday (struct timespec *tv);
extern void getnstimestamp(struct timespec *ts);
extern struct timespec timespec_trunc(struct timespec t, unsigned gran);
......
......@@ -561,6 +561,28 @@ void getnstimeofday(struct timespec *tv)
EXPORT_SYMBOL_GPL(getnstimeofday);
#endif
void getnstimestamp(struct timespec *ts)
{
unsigned int seq;
struct timespec wall2mono;
/* synchronize with settimeofday() changes */
do {
seq = read_seqbegin(&xtime_lock);
getnstimeofday(ts);
wall2mono = wall_to_monotonic;
} while(unlikely(read_seqretry(&xtime_lock, seq)));
/* adjust to monotonicaly-increasing values */
ts->tv_sec += wall2mono.tv_sec;
ts->tv_nsec += wall2mono.tv_nsec;
while (unlikely(ts->tv_nsec >= NSEC_PER_SEC)) {
ts->tv_nsec -= NSEC_PER_SEC;
ts->tv_sec++;
}
}
EXPORT_SYMBOL_GPL(getnstimestamp);
#if (BITS_PER_LONG < 64)
u64 get_jiffies_64(void)
{
......
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