netdev - [patch V2 04/26] timekeeping: Introduce timekeeper ID

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Message-ID: <20250519083025.842476378@linutronix.de>
Date: Mon, 19 May 2025 10:33:19 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: netdev@...r.kernel.org,
 Richard Cochran <richardcochran@...il.com>,
 Christopher Hall <christopher.s.hall@...el.com>,
 John Stultz <jstultz@...gle.com>,
 Frederic Weisbecker <frederic@...nel.org>,
 Anna-Maria Behnsen <anna-maria@...utronix.de>,
 Miroslav Lichvar <mlichvar@...hat.com>,
 Werner Abt <werner.abt@...nberg-usa.com>,
 David Woodhouse <dwmw2@...radead.org>,
 Stephen Boyd <sboyd@...nel.org>,
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
 Kurt Kanzenbach <kurt@...utronix.de>,
 Nam Cao <namcao@...utronix.de>,
 Antoine Tenart <atenart@...nel.org>
Subject: [patch V2 04/26] timekeeping: Introduce timekeeper ID

From: Anna-Maria Behnsen <anna-maria@...utronix.de>

As long as there is only a single timekeeper, there is no need to clarify
which timekeeper is used. But with the upcoming reusage of the timekeeper
infrastructure for auxiliary clock timekeepers, an ID is required to
differentiate.

Introduce an enum for timekeeper IDs, introduce a field in struct tk_data
to store this timekeeper id and add also initialization. The id struct
field is added at the end of the second cachline, as there is a 4 byte hole
anyway.

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

---
 include/linux/timekeeper_internal.h |   14 +++++++++++++-
 kernel/time/timekeeping.c           |    5 +++--
 2 files changed, 16 insertions(+), 3 deletions(-)
---
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -12,6 +12,16 @@
 #include <linux/time.h>
 
 /**
+ * timekeeper_ids - IDs for various time keepers in the kernel
+ * @TIMEKEEPER_CORE:	The central core timekeeper managing system time
+ * @TIMEKEEPERS_MAX:	The maximum number of timekeepers managed
+ */
+enum timekeeper_ids {
+	TIMEKEEPER_CORE,
+	TIMEKEEPERS_MAX,
+};
+
+/**
  * struct tk_read_base - base structure for timekeeping readout
  * @clock:	Current clocksource used for timekeeping.
  * @mask:	Bitmask for two's complement subtraction of non 64bit clocks
@@ -52,6 +62,7 @@ struct tk_read_base {
  * @offs_boot:			Offset clock monotonic -> clock boottime
  * @offs_tai:			Offset clock monotonic -> clock tai
  * @coarse_nsec:		The nanoseconds part for coarse time getters
+ * @id:				The timekeeper ID
  * @tkr_raw:			The readout base structure for CLOCK_MONOTONIC_RAW
  * @raw_sec:			CLOCK_MONOTONIC_RAW  time in seconds
  * @clock_was_set_seq:		The sequence number of clock was set events
@@ -101,7 +112,7 @@ struct tk_read_base {
  * which results in the following cacheline layout:
  *
  * 0:	seqcount, tkr_mono
- * 1:	xtime_sec ... coarse_nsec
+ * 1:	xtime_sec ... id
  * 2:	tkr_raw, raw_sec
  * 3,4: Internal variables
  *
@@ -123,6 +134,7 @@ struct timekeeper {
 	ktime_t			offs_boot;
 	ktime_t			offs_tai;
 	u32			coarse_nsec;
+	enum timekeeper_ids	id;
 
 	/* Cacheline 2: */
 	struct tk_read_base	tkr_raw;
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1663,10 +1663,11 @@ read_persistent_wall_and_boot_offset(str
 	*boot_offset = ns_to_timespec64(local_clock());
 }
 
-static __init void tkd_basic_setup(struct tk_data *tkd)
+static __init void tkd_basic_setup(struct tk_data *tkd, enum timekeeper_ids tk_id)
 {
 	raw_spin_lock_init(&tkd->lock);
 	seqcount_raw_spinlock_init(&tkd->seq, &tkd->lock);
+	tkd->timekeeper.id = tkd->shadow_timekeeper.id = tk_id;
 }
 
 /*
@@ -1696,7 +1697,7 @@ void __init timekeeping_init(void)
 	struct timekeeper *tks = &tk_core.shadow_timekeeper;
 	struct clocksource *clock;
 
-	tkd_basic_setup(&tk_core);
+	tkd_basic_setup(&tk_core, TIMEKEEPER_CORE);
 
 	read_persistent_wall_and_boot_offset(&wall_time, &boot_offset);
 	if (timespec64_valid_settod(&wall_time) &&