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[PATCH] Add getnstimestamp function

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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: Matt Helsley <matthltc@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Matt Helsley 2005-12-12 00:37:09 -08:00 committed by Linus Torvalds
parent 894ec8707c
commit 64123fd42c
2 changed files with 23 additions and 0 deletions
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1
include/linux/time.h
View file

@ -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);

22
kernel/time.c
View file

@ -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)
{