[PATCH v2 1/2] timekeeping: Introduce a fast boot clock derived from fast monotonic clock

[Joel Fernandes <joelaf@google.com>]

Introduce a fast boot clock. It accounts for suspend time and is based on the
fast monotonic clock so that its safe to use for tracing. Next patch adds the
clock to trace clock.

Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Joel Fernandes <joelaf@google.com>
---
 kernel/time/timekeeping.c | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 37dec7e..5a3f5ff 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -56,6 +56,12 @@ static struct timekeeper shadow_timekeeper;
 struct tk_fast {
 	seqcount_t		seq;
 	struct tk_read_base	base[2];
+
+	/*
+	 * first dimension is based on lower seq bit,
+	 * second dimension is for offset type (real, boot, tai)
+	 */
+	ktime_t			offsets[2][TK_OFFS_MAX];
 };
 
 static struct tk_fast tk_fast_mono ____cacheline_aligned;
@@ -350,14 +356,20 @@ static void update_fast_timekeeper(struct tk_read_base *tkr, struct tk_fast *tkf
 	/* Force readers off to base[1] */
 	raw_write_seqcount_latch(&tkf->seq);
 
-	/* Update base[0] */
+	/* Update base[0] and offsets*/
 	memcpy(base, tkr, sizeof(*base));
+	tkf->offsets[0][TK_OFFS_REAL] = tk_core.timekeeper.offs_real;
+	tkf->offsets[0][TK_OFFS_BOOT] = tk_core.timekeeper.offs_boot;
+	tkf->offsets[0][TK_OFFS_TAI] = tk_core.timekeeper.offs_tai;
 
 	/* Force readers back to base[0] */
 	raw_write_seqcount_latch(&tkf->seq);
 
-	/* Update base[1] */
+	/* Update base[1] and offsets*/
 	memcpy(base + 1, base, sizeof(*base));
+	tkf->offsets[1][TK_OFFS_REAL] = tk_core.timekeeper.offs_real;
+	tkf->offsets[1][TK_OFFS_BOOT] = tk_core.timekeeper.offs_boot;
+	tkf->offsets[1][TK_OFFS_TAI] = tk_core.timekeeper.offs_tai;
 }
 
 /**
@@ -392,16 +404,23 @@ static void update_fast_timekeeper(struct tk_read_base *tkr, struct tk_fast *tkf
  * of the following timestamps. Callers need to be aware of that and
  * deal with it.
  */
-static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf)
+static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf, int offset)
 {
 	struct tk_read_base *tkr;
 	unsigned int seq;
 	u64 now;
+	ktime_t *off;
 
 	do {
 		seq = raw_read_seqcount_latch(&tkf->seq);
 		tkr = tkf->base + (seq & 0x01);
-		now = ktime_to_ns(tkr->base);
+
+		if (unlikely((offset >= 0))) {
+			off = tkf->offsets[seq & 0x01];
+			now = ktime_to_ns(ktime_add(tkr->base, off[offset]));
+		} else {
+			now = ktime_to_ns(tkr->base);
+		}
 
 		now += timekeeping_delta_to_ns(tkr,
 				clocksource_delta(
@@ -415,16 +434,21 @@ static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf)
 
 u64 ktime_get_mono_fast_ns(void)
 {
-	return __ktime_get_fast_ns(&tk_fast_mono);
+	return __ktime_get_fast_ns(&tk_fast_mono, -1);
 }
 EXPORT_SYMBOL_GPL(ktime_get_mono_fast_ns);
 
 u64 ktime_get_raw_fast_ns(void)
 {
-	return __ktime_get_fast_ns(&tk_fast_raw);
+	return __ktime_get_fast_ns(&tk_fast_raw, -1);
 }
 EXPORT_SYMBOL_GPL(ktime_get_raw_fast_ns);
 
+u64 ktime_get_boot_fast_ns(void)
+{
+	return __ktime_get_fast_ns(&tk_fast_mono, TK_OFFS_BOOT);
+}
+
 /* Suspend-time cycles value for halted fast timekeeper. */
 static cycle_t cycles_at_suspend;
 
-- 
2.8.0.rc3.226.g39d4020