time: Provide get_xtime_and_monotonic_offset()

The hrtimer code accesses timekeeping variables under
xtime_lock. Provide a sensible accessor function and use it.

[ tglx: Removed the conditionals, unused variable, fixed codingstyle
  	and massaged changelog ]

Signed-off-by: Torben Hohn <torbenh@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: johnstul@us.ibm.com
Cc: yong.zhang0@gmail.com
Cc: hch@infradead.org
LKML-Reference: <20110127145905.23248.30458.stgit@localhost>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/time.h

@@ -127,6 +127,7 @@ struct timespec current_kernel_time(void);
 struct timespec __current_kernel_time(void); /* does not take xtime_lock */
 struct timespec __get_wall_to_monotonic(void); /* does not take xtime_lock */
 struct timespec get_monotonic_coarse(void);
+void get_xtime_and_monotonic_offset(struct timespec *xtim, struct timespec *wtom);
 
 #define CURRENT_TIME		(current_kernel_time())
 #define CURRENT_TIME_SEC	((struct timespec) { get_seconds(), 0 })

kernel/hrtimer.c

@@ -85,13 +85,8 @@ static void hrtimer_get_softirq_time(struct hrtimer_cpu_base *base)
 {
 	ktime_t xtim, tomono;
 	struct timespec xts, tom;
-	unsigned long seq;
 
-	do {
+	get_xtime_and_monotonic_offset(&xts, &tom);
-		seq = read_seqbegin(&xtime_lock);
-		xts = __current_kernel_time();
-		tom = __get_wall_to_monotonic();
-	} while (read_seqretry(&xtime_lock, seq));
 
 	xtim = timespec_to_ktime(xts);
 	tomono = timespec_to_ktime(tom);
@@ -612,15 +607,11 @@ static void retrigger_next_event(void *arg)
 {
 	struct hrtimer_cpu_base *base;
 	struct timespec realtime_offset, wtm;
-	unsigned long seq;
 
 	if (!hrtimer_hres_active())
 		return;
 
-	do {
+	get_xtime_and_monotonic_offset(&realtime_offset, &wtm);
-		seq = read_seqbegin(&xtime_lock);
-		wtm = __get_wall_to_monotonic();
-	} while (read_seqretry(&xtime_lock, seq));
 	set_normalized_timespec(&realtime_offset, -wtm.tv_sec, -wtm.tv_nsec);
 
 	base = &__get_cpu_var(hrtimer_bases);

kernel/time/timekeeping.c

@@ -958,3 +958,19 @@ void do_timer(unsigned long ticks)
 	update_wall_time();
 	calc_global_load(ticks);
 }
+
+/**
+ * get_xtime_and_monotonic_offset() - get xtime and wall_to_monotonic
+ * @xtim:	pointer to timespec to be set with xtime
+ * @wtom:	pointer to timespec to be set with wall_to_monotonic
+ */
+void get_xtime_and_monotonic_offset(struct timespec *xtim, struct timespec *wtom)
+{
+	unsigned long seq;
+
+	do {
+		seq = read_seqbegin(&xtime_lock);
+		*xtim = xtime;
+		*wtom = wall_to_monotonic;
+	} while (read_seqretry(&xtime_lock, seq));
+}