linux-kernel - [PATCH] timekeeping: add get_jiffies_boot

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Message-Id: <20190614094831.14087-1-Jason@zx2c4.com>
Date:   Fri, 14 Jun 2019 11:48:31 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-kernel@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH] timekeeping: add get_jiffies_boot_64() for jiffies including sleep

This enables using the usual get_jiffies_64() but taking into account
time spent sleeping, giving the high performance characteristics of
querying jiffies without the drawback.

We accomplish this by precomputing the boottime jiffies offset whenever
it is updated, rather than doing the expensive-ish div_u64 on each
query.

Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Arnd Bergmann <arnd@...db.de>
---
 include/linux/timekeeper_internal.h |  2 ++
 include/linux/timekeeping.h         |  2 ++
 kernel/time/timekeeping.c           | 12 ++++++++++++
 3 files changed, 16 insertions(+)

diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index 7acb953298a7..2e4c52fe0250 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -51,6 +51,7 @@ struct tk_read_base {
  * @wall_to_monotonic:	CLOCK_REALTIME to CLOCK_MONOTONIC offset
  * @offs_real:		Offset clock monotonic -> clock realtime
  * @offs_boot:		Offset clock monotonic -> clock boottime
+ * @offs_boot_jiffies64	Offset clock monotonic -> clock boottime in jiffies64
  * @offs_tai:		Offset clock monotonic -> clock tai
  * @tai_offset:		The current UTC to TAI offset in seconds
  * @clock_was_set_seq:	The sequence number of clock was set events
@@ -93,6 +94,7 @@ struct timekeeper {
 	struct timespec64	wall_to_monotonic;
 	ktime_t			offs_real;
 	ktime_t			offs_boot;
+	u64			offs_boot_jiffies64;
 	ktime_t			offs_tai;
 	s32			tai_offset;
 	unsigned int		clock_was_set_seq;
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index a8ab0f143ac4..511803c9cae2 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -151,6 +151,8 @@ extern u64 ktime_get_raw_fast_ns(void);
 extern u64 ktime_get_boot_fast_ns(void);
 extern u64 ktime_get_real_fast_ns(void);
 
+extern u64 get_jiffies_boot_64(void);
+
 /*
  * timespec64/time64_t interfaces utilizing the ktime based ones
  * for API completeness, these could be implemented more efficiently
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 85f5912d8f70..83c675bcd88a 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -146,6 +146,7 @@ static void tk_set_wall_to_mono(struct timekeeper *tk, struct timespec64 wtm)
 static inline void tk_update_sleep_time(struct timekeeper *tk, ktime_t delta)
 {
 	tk->offs_boot = ktime_add(tk->offs_boot, delta);
+	tk->offs_boot_jiffies64 = nsecs_to_jiffies64(ktime_to_ns(tk->offs_boot));
 }
 
 /*
@@ -539,6 +540,17 @@ u64 ktime_get_real_fast_ns(void)
 }
 EXPORT_SYMBOL_GPL(ktime_get_real_fast_ns);
 
+/**
+ * get_jiffies_boot_64 - The normal get_jiffies_64(), but taking into
+ * account the time spent sleeping. This does not do any sort of locking
+ * on the time spent sleeping.
+ */
+u64 get_jiffies_boot_64(void)
+{
+	return get_jiffies_64() + tk_core.timekeeper.offs_boot_jiffies64;
+}
+EXPORT_SYMBOL(get_jiffies_boot_64);
+
 /**
  * halt_fast_timekeeper - Prevent fast timekeeper from accessing clocksource.
  * @tk: Timekeeper to snapshot.
-- 
2.21.0