linux-kernel - [PATCH v8 2/8] time: Add timekeeping snapshot code capturing system time and counter

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Message-Id: <1456139726-3327-3-git-send-email-christopher.s.hall@intel.com>
Date:	Mon, 22 Feb 2016 03:15:20 -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, kevin.j.clarke@...el.com
Subject: [PATCH v8 2/8] time: 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>
[jstultz: Moved structure definitions around to clean things up]
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
 include/linux/timekeeping.h | 18 ++++++++++++++++++
 kernel/time/timekeeping.c   | 30 ++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index ec89d84..af220e1 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -267,6 +267,24 @@ extern void ktime_get_raw_and_real_ts64(struct timespec64 *ts_raw,
 				        struct timespec64 *ts_real);
 
 /*
+ * 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;
+};
+
+/*
+ * Simultaneously snapshot realtime and monotonic raw clocks
+ */
+extern void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot);
+
+/*
  * Persistent clock related interfaces
  */
 extern int persistent_clock_is_local;
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 4243d28..89b4695 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -874,6 +874,36 @@ time64_t __ktime_get_real_seconds(void)
 	return tk->xtime_sec;
 }
 
+/**
+ * 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