timekeeping: Increase granularity of read_persistent_clock()
The persistent clock of some architectures (e.g. s390) have a
better granularity than seconds. To reduce the delta between the
host clock and the guest clock in a virtualized system change the
read_persistent_clock function to return a struct timespec.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134811.013873340@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index e76c2e7..a94ec48 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -182,12 +182,9 @@
static void etr_reset(void);
static void stp_reset(void);
-unsigned long read_persistent_clock(void)
+void read_persistent_clock(struct timespec *ts)
{
- struct timespec ts;
-
- tod_to_timeval(get_clock() - TOD_UNIX_EPOCH, &ts);
- return ts.tv_sec;
+ tod_to_timeval(get_clock() - TOD_UNIX_EPOCH, ts);
}
static cycle_t read_tod_clock(struct clocksource *cs)
@@ -248,7 +245,6 @@
{
struct timespec ts;
unsigned long flags;
- cycle_t now;
/* Reset time synchronization interfaces. */
etr_reset();
@@ -266,20 +262,10 @@
panic("Could not register TOD clock source");
/*
- * The TOD clock is an accurate clock. The xtime should be
- * initialized in a way that the difference between TOD and
- * xtime is reasonably small. Too bad that timekeeping_init
- * sets xtime.tv_nsec to zero. In addition the clock source
- * change from the jiffies clock source to the TOD clock
- * source add another error of up to 1/HZ second. The same
- * function sets wall_to_monotonic to a value that is too
- * small for /proc/uptime to be accurate.
- * Reset xtime and wall_to_monotonic to sane values.
+ * Reset wall_to_monotonic to the initial timestamp created
+ * in head.S to get a precise value in /proc/uptime.
*/
write_seqlock_irqsave(&xtime_lock, flags);
- now = get_clock();
- tod_to_timeval(now - TOD_UNIX_EPOCH, &xtime);
- clocksource_tod.cycle_last = now;
tod_to_timeval(sched_clock_base_cc - TOD_UNIX_EPOCH, &ts);
set_normalized_timespec(&wall_to_monotonic, -ts.tv_sec, -ts.tv_nsec);
write_sequnlock_irqrestore(&xtime_lock, flags);