[RFC][PATCH 001/002] Add getnstimestamp function

Matt Helsley
2005-12-06T05:15:47Z

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>

--

Index: linux-2.6.15-rc5/kernel/time.c
===================================================================
--- linux-2.6.15-rc5.orig/kernel/time.c
+++ linux-2.6.15-rc5/kernel/time.c
@@ -562,10 +562,32 @@ void getnstimeofday(struct timespec *tv)
tv->tv_nsec = x.tv_usec * NSEC_PER_USEC;
}
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);
+
/* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
* Assumes input in normal date format, i.e. 1980-12-31 23:59:59
* => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
*
* [For the Julian calendar (which was used in Russia before 1917,
Index: linux-2.6.15-rc5/include/linux/time.h
===================================================================
--- linux-2.6.15-rc5.orig/include/linux/time.h
+++ linux-2.6.15-rc5/include/linux/time.h
@@ -78,10 +78,11 @@ extern long do_utimes(char __user *filen
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);

/**
* timespec_to_ns - Convert timespec to nanoseconds