include/linux/timekeeping.h | 34 +++++++++----- kernel/time/timekeeping.c | 89 ++++++++++++++++++++++++++---------- 2 files changed, 90 insertions(+), 33 deletions(-)
The following commit has been merged into the timers/ptp branch of tip:
Commit-ID: eba302268a019275fd6ff452d4ff0b94fef11c76
Gitweb: https://git.kernel.org/tip/eba302268a019275fd6ff452d4ff0b94fef11c76
Author: Thomas Gleixner <tglx@kernel.org>
AuthorDate: Fri, 29 May 2026 21:59:51 +02:00
Committer: Thomas Gleixner <tglx@kernel.org>
CommitterDate: Tue, 02 Jun 2026 11:39:57 +02:00
timekeeping: Provide ktime_get_snapshot_id()
ktime_get_snapshot() provides a snapshot of the underlying clocksource
counter value and the corresponding CLOCK_MONOTONIC_RAW, CLOCK_REALTIME and
CLOCK_BOOTTIME timestamps.
There is no usage of CLOCK_REALTIME and CLOCK_BOOTTIME at the same time and
CLOCK_BOOTTIME support was just added for the ARM64 KVM tracing mechanism,
which needs CLOCK_BOOTTIME and the underlying clocksource counter value.
ktime_get_snapshot() is also not suitable for usage with CLOCK_AUX, but
that's a prerequisite to support PTP hardware timestamping for CLOCK_AUX
steering.
As a first step, rename ktime_get_snapshot() to ktime_get_snapshot_id(),
which now takes a clockid argument to select the clock which needs to be
captured. The result is stored in system_time_snapshot::systime, which will
replace the system_time_snapshot::real/boot members once all usage sites
have been converted.
ktime_get_snapshot() is a simple wrapper which hands in CLOCK_REALTIME as
clockid argument for the conversion period. That means CLOCK_REALTIME is
now captured twice, but that redunancy is only temporary.
As all usage sites of struct system_time_snapshot has to be updated anyway,
rename the 'raw' member to 'monoraw' for clarity.
No functional change vs. current users of ktime_get_snapshot()
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: David Woodhouse <dwmw@amazon.co.uk>
Tested-by: Arthur Kiyanovski <akiyano@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20260529195556.971591633@kernel.org
---
include/linux/timekeeping.h | 34 +++++++++-----
kernel/time/timekeeping.c | 89 ++++++++++++++++++++++++++----------
2 files changed, 90 insertions(+), 33 deletions(-)
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index aee2c1a..161157c 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -276,24 +276,32 @@ static inline bool ktime_get_aux_ts64(clockid_t id, struct timespec64 *kt) { ret
#endif
/**
- * 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
- * @boot: Boot time
- * @raw: Monotonic raw system time
- * @cs_id: Clocksource ID
+ * struct system_time_snapshot - Simultaneous time capture of CLOCK_MONOTONIC_RAW,
+ * a selected CLOCK_* and the clocksource counter value
+ * @cycles: Clocksource counter value to produce the system times
+ * @systime: The system time of the selected CLOCK ID
+ * @real: Realtime system time
+ * @boot: Boot time
+ * @raw: Monotonic raw system time
+ * @monoraw: Monotonic raw system time
+ * @cs_id: Clocksource ID
* @clock_was_set_seq: The sequence number of clock-was-set events
* @cs_was_changed_seq: The sequence number of clocksource change events
+ * @valid: True if the snapshot is valid
*/
struct system_time_snapshot {
u64 cycles;
+ ktime_t systime;
ktime_t real;
ktime_t boot;
- ktime_t raw;
+ union {
+ ktime_t raw;
+ ktime_t monoraw;
+ };
enum clocksource_ids cs_id;
unsigned int clock_was_set_seq;
u8 cs_was_changed_seq;
+ u8 valid;
};
/**
@@ -341,9 +349,15 @@ extern int get_device_system_crosststamp(
struct system_device_crosststamp *xtstamp);
/*
- * Simultaneously snapshot realtime and monotonic raw clocks
+ * Simultaneously snapshot a given clock with MONOTONIC_RAW and the underlying
+ * clocksource counter value.
*/
-extern void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot);
+extern void ktime_get_snapshot_id(clockid_t clock_id, struct system_time_snapshot *systime_snapshot);
+
+static inline void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot)
+{
+ ktime_get_snapshot_id(CLOCK_REALTIME, systime_snapshot);
+}
/*
* Persistent clock related interfaces
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index c493a40..0053dc0 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1183,43 +1183,86 @@ noinstr time64_t __ktime_get_real_seconds(void)
}
/**
- * 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;
+ * ktime_get_snapshot_id - Simultaneously snapshot a given clock ID with
+ * CLOCK_MONOTONIC_RAW and the underlying
+ * clocksource counter value.
+ * @clock_id: The clock ID to snapshot
+ * @systime_snapshot: Pointer to struct receiving the system time snapshot
+ */
+void ktime_get_snapshot_id(clockid_t clock_id, struct system_time_snapshot *systime_snapshot)
+{
+ ktime_t base_raw, base_sys, offs_sys, *offs, offs_zero = 0;
+ u64 nsec_raw, nsec_sys, now;
+ struct timekeeper *tk;
+ struct tk_data *tkd;
unsigned int seq;
- ktime_t base_raw;
ktime_t base_real;
ktime_t base_boot;
- u64 nsec_raw;
- u64 nsec_real;
- u64 now;
- WARN_ON_ONCE(timekeeping_suspended);
+ /* Invalidate the snapshot for all failure cases */
+ systime_snapshot->valid = false;
+
+ if (WARN_ON_ONCE(timekeeping_suspended))
+ return;
+
+ switch (clock_id) {
+ case CLOCK_REALTIME:
+ tkd = &tk_core;
+ offs = &tk_core.timekeeper.offs_real;
+ break;
+ /* Map RAW to MONOTONIC so the loop below is trivial */
+ case CLOCK_MONOTONIC_RAW:
+ case CLOCK_MONOTONIC:
+ tkd = &tk_core;
+ offs = &offs_zero;
+ break;
+ case CLOCK_BOOTTIME:
+ tkd = &tk_core;
+ offs = &tk_core.timekeeper.offs_boot;
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ return;
+ }
+
+ tk = &tkd->timekeeper;
do {
- seq = read_seqcount_begin(&tk_core.seq);
+ seq = read_seqcount_begin(&tkd->seq);
+
now = tk_clock_read(&tk->tkr_mono);
systime_snapshot->cs_id = tk->tkr_mono.clock->id;
systime_snapshot->cs_was_changed_seq = tk->cs_was_changed_seq;
systime_snapshot->clock_was_set_seq = tk->clock_was_set_seq;
- base_real = ktime_add(tk->tkr_mono.base,
- tk_core.timekeeper.offs_real);
- base_boot = ktime_add(tk->tkr_mono.base,
- tk_core.timekeeper.offs_boot);
+
+ base_sys = tk->tkr_mono.base;
+ offs_sys = *offs;
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));
+
+ /* Kept around until the callers are fixed up */
+ base_real = ktime_add(base_sys, tk_core.timekeeper.offs_real);
+ base_boot = ktime_add(base_sys, tk_core.timekeeper.offs_boot);
+
+ nsec_sys = timekeeping_cycles_to_ns(&tk->tkr_mono, now);
+ nsec_raw = timekeeping_cycles_to_ns(&tk->tkr_raw, now);
+ } while (read_seqcount_retry(&tkd->seq, seq));
systime_snapshot->cycles = now;
- systime_snapshot->real = ktime_add_ns(base_real, nsec_real);
- systime_snapshot->boot = ktime_add_ns(base_boot, nsec_real);
- systime_snapshot->raw = ktime_add_ns(base_raw, nsec_raw);
+ systime_snapshot->systime = ktime_add_ns(base_sys, offs_sys + nsec_sys);
+ systime_snapshot->real = ktime_add_ns(base_real, nsec_sys);
+ systime_snapshot->boot = ktime_add_ns(base_boot, nsec_sys);
+ systime_snapshot->monoraw = ktime_add_ns(base_raw, nsec_raw);
+
+ /*
+ * Special case for PTP. Just transfer the raw time into sys,
+ * so the call sites can consistently use snap::systime.
+ */
+ if (clock_id == CLOCK_MONOTONIC_RAW)
+ systime_snapshot->systime = systime_snapshot->monoraw;
+ /* Tell the consumer that this snapshot is valid */
+ systime_snapshot->valid = true;
}
-EXPORT_SYMBOL_GPL(ktime_get_snapshot);
+EXPORT_SYMBOL_GPL(ktime_get_snapshot_id);
/* Scale base by mult/div checking for overflow */
static int scale64_check_overflow(u64 mult, u64 div, u64 *base)© 2016 - 2026 Red Hat, Inc.