timekeeping: Provide internal ktime_t based data

The ktime_t based interfaces are used a lot in performance critical
code pathes. Add ktime_t based data so the interfaces don't have to
convert from the xtime/timespec based data.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>

2 files changed, 25 insertions, 0 deletions

diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index 2cb96235c249..87e0992564f2 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -36,6 +36,9 @@ struct timekeeper {
         /* Clock shifted nano seconds */
         u64                     xtime_nsec;
 
+        /* Monotonic base time */
+        ktime_t                 base_mono;
+
         /* Current CLOCK_REALTIME time in seconds */
         u64                     xtime_sec;
         /* CLOCK_REALTIME to CLOCK_MONOTONIC offset */
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index bfe3ea09afc9..86a92476c027 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -291,6 +291,26 @@ int pvclock_gtod_unregister_notifier(struct notifier_block *nb)
 }
 EXPORT_SYMBOL_GPL(pvclock_gtod_unregister_notifier);
 
+/*
+ * Update the ktime_t based scalar nsec members of the timekeeper
+ */
+static inline void tk_update_ktime_data(struct timekeeper *tk)
+{
+        s64 nsec;
+
+        /*
+         * The xtime based monotonic readout is:
+         *      nsec = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec + now();
+         * The ktime based monotonic readout is:
+         *      nsec = base_mono + now();
+         * ==> base_mono = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec
+         */
+        nsec = (s64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec);
+        nsec *= NSEC_PER_SEC;
+        nsec += tk->wall_to_monotonic.tv_nsec;
+        tk->base_mono = ns_to_ktime(nsec);
+}
+
 /* must hold timekeeper_lock */
 static void timekeeping_update(struct timekeeper *tk, unsigned int action)
 {
@@ -301,6 +321,8 @@ static void timekeeping_update(struct timekeeper *tk, unsigned int action)
         update_vsyscall(tk);
         update_pvclock_gtod(tk, action & TK_CLOCK_WAS_SET);
 
+        tk_update_ktime_data(tk);
+
         if (action & TK_MIRROR)
                 memcpy(&shadow_timekeeper, &tk_core.timekeeper,
                        sizeof(tk_core.timekeeper));