linux-kernel - [PATCH v6 5/9] Add timekeeping snapshot code capturing system time and counter

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Date:	Wed, 13 Jan 2016 04:12:25 -0800
From:	"Christopher S. Hall" <christopher.s.hall@...el.com>
To:	tglx@...utronix.de, richardcochran@...il.com, mingo@...hat.com,
	john.stultz@...aro.org, hpa@...or.com, jeffrey.t.kirsher@...el.com
Cc:	"Christopher S. Hall" <christopher.s.hall@...el.com>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
	kevin.b.stanton@...el.com
Subject: [PATCH v6 5/9] Add timekeeping snapshot code capturing system time and counter

In the current timekeeping code there isn't any interface to
atomically capture the current relationship between the system counter
and system time. ktime_get_snapshot() returns this triple (counter,
monotonic raw, realtime) in the system_time_snapshot struct.

Signed-off-by: Christopher S. Hall <christopher.s.hall@...el.com>
---
 include/linux/clocksource.h | 13 +++++++++++++
 include/linux/timekeeping.h |  6 ++++++
 kernel/time/timekeeping.c   | 31 +++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+)

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 726ca68..cccbd1c 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -281,4 +281,17 @@ struct correlated_cs {
 					   cycle_t cycles);
 };
 
+/*
+ * struct system_time_snapshot - simultaneous raw/real time capture with
+ *	counter value
+ * @cycles:	Clocksource counter value to produce the system times
+ * @real:	Realtime system time
+ * @raw:	Monotonic raw system time
+ */
+struct system_time_snapshot {
+	cycles_t	cycles;
+	ktime_t		real;
+	ktime_t		raw;
+};
+
 #endif /* _LINUX_CLOCKSOURCE_H */
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 2651e0a..f5fe657 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -301,6 +301,12 @@ struct sync_device_time_cb {
 extern int get_device_system_crosststamp(struct sync_device_time_cb *cb,
 					 struct system_device_crosststamp *ts);
 
+struct system_time_snapshot;
+/*
+ * Simultaneously snapshot realtime and monotonic raw clocks
+ */
+extern void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot);
+
 /*
  * Persistent clock related interfaces
  */
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 84534f8..26049df 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -862,6 +862,37 @@ time64_t ktime_get_real_seconds(void)
 }
 EXPORT_SYMBOL_GPL(ktime_get_real_seconds);
 
+/**
+ * ktime_get_snapshot - snapshots the realtime/monotonic raw clocks with counter
+ * @systime_snapshot:	pointer to struct receiving the system time snapshot
+ */
+void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot)
+{
+	struct timekeeper *tk = &tk_core.timekeeper;
+	unsigned long seq;
+	ktime_t base_raw;
+	ktime_t base_real;
+	s64 nsec_raw;
+	s64 nsec_real;
+	cycle_t now;
+
+	do {
+		seq = read_seqcount_begin(&tk_core.seq);
+
+		now = tk->tkr_mono.read(tk->tkr_mono.clock);
+		base_real = ktime_add(tk->tkr_mono.base,
+				      tk_core.timekeeper.offs_real);
+		base_raw = tk->tkr_raw.base;
+		nsec_real = timekeeping_cycles_to_ns(&tk->tkr_mono, now);
+		nsec_raw  = timekeeping_cycles_to_ns(&tk->tkr_raw, now);
+	} while (read_seqcount_retry(&tk_core.seq, seq));
+
+	systime_snapshot->cycles = now;
+	systime_snapshot->real = ktime_add_ns(base_real, nsec_real);
+	systime_snapshot->raw = ktime_add_ns(base_raw, nsec_raw);
+}
+EXPORT_SYMBOL_GPL(ktime_get_snapshot);
+
 #ifdef CONFIG_NTP_PPS
 
 /**
-- 
2.1.4