[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <175689353303.1920.4835241898909824126.tip-bot2@tip-bot2>
Date: Wed, 03 Sep 2025 09:58:53 -0000
From: tip-bot2 for Thomas Weißschuh <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Miroslav Lichvar <mlichvar@...hat.com>, thomas.weissschuh@...utronix.de,
Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: timers/urgent] vdso/vsyscall: Avoid slow division loop in
auxiliary clock update
The following commit has been merged into the timers/urgent branch of tip:
Commit-ID: 762af5a2aa0ad18da1316666dae30d369268d44c
Gitweb: https://git.kernel.org/tip/762af5a2aa0ad18da1316666dae30d369268d44c
Author: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
AuthorDate: Mon, 25 Aug 2025 15:26:35 +02:00
Committer: Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Wed, 03 Sep 2025 11:55:11 +02:00
vdso/vsyscall: Avoid slow division loop in auxiliary clock update
The call to __iter_div_u64_rem() in vdso_time_update_aux() is a wrapper
around subtraction. It cannot be used to divide large numbers, as that
introduces long, computationally expensive delays. A regular u64 division
is also not possible in the timekeeper update path as it can be too slow.
Instead of splitting the ktime_t offset into into second and subsecond
components during the timekeeper update fast-path, do it together with the
adjustment of tk->offs_aux in the slow-path. Equivalent to the handling of
offs_boot and monotonic_to_boot.
Reuse the storage of monotonic_to_boot for the new field, as it is not used
by auxiliary timekeepers.
Fixes: 380b84e168e5 ("vdso/vsyscall: Update auxiliary clock data in the datapage")
Reported-by: Miroslav Lichvar <mlichvar@...hat.com>
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/all/20250825-vdso-auxclock-division-v1-1-a1d32a16a313@linutronix.de
Closes: https://lore.kernel.org/lkml/aKwsNNWsHJg8IKzj@localhost/
---
include/linux/timekeeper_internal.h | 9 ++++++++-
kernel/time/timekeeping.c | 10 ++++++++--
kernel/time/vsyscall.c | 4 ++--
3 files changed, 18 insertions(+), 5 deletions(-)
diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index c27aac6..b8ae89e 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -76,6 +76,7 @@ struct tk_read_base {
* @cs_was_changed_seq: The sequence number of clocksource change events
* @clock_valid: Indicator for valid clock
* @monotonic_to_boot: CLOCK_MONOTONIC to CLOCK_BOOTTIME offset
+ * @monotonic_to_aux: CLOCK_MONOTONIC to CLOCK_AUX offset
* @cycle_interval: Number of clock cycles in one NTP interval
* @xtime_interval: Number of clock shifted nano seconds in one NTP
* interval.
@@ -117,6 +118,9 @@ struct tk_read_base {
* @offs_aux is used by the auxiliary timekeepers which do not utilize any
* of the regular timekeeper offset fields.
*
+ * @monotonic_to_aux is a timespec64 representation of @offs_aux to
+ * accelerate the VDSO update for CLOCK_AUX.
+ *
* The cacheline ordering of the structure is optimized for in kernel usage of
* the ktime_get() and ktime_get_ts64() family of time accessors. Struct
* timekeeper is prepended in the core timekeeping code with a sequence count,
@@ -159,7 +163,10 @@ struct timekeeper {
u8 cs_was_changed_seq;
u8 clock_valid;
- struct timespec64 monotonic_to_boot;
+ union {
+ struct timespec64 monotonic_to_boot;
+ struct timespec64 monotonic_to_aux;
+ };
u64 cycle_interval;
u64 xtime_interval;
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 059fa8b..b6974fc 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -83,6 +83,12 @@ static inline bool tk_is_aux(const struct timekeeper *tk)
}
#endif
+static inline void tk_update_aux_offs(struct timekeeper *tk, ktime_t offs)
+{
+ tk->offs_aux = offs;
+ tk->monotonic_to_aux = ktime_to_timespec64(offs);
+}
+
/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;
@@ -1506,7 +1512,7 @@ static int __timekeeping_inject_offset(struct tk_data *tkd, const struct timespe
timekeeping_restore_shadow(tkd);
return -EINVAL;
}
- tks->offs_aux = offs;
+ tk_update_aux_offs(tks, offs);
}
timekeeping_update_from_shadow(tkd, TK_UPDATE_ALL);
@@ -2937,7 +2943,7 @@ static int aux_clock_set(const clockid_t id, const struct timespec64 *tnew)
* xtime ("realtime") is not applicable for auxiliary clocks and
* kept in sync with "monotonic".
*/
- aux_tks->offs_aux = ktime_sub(timespec64_to_ktime(*tnew), tnow);
+ tk_update_aux_offs(aux_tks, ktime_sub(timespec64_to_ktime(*tnew), tnow));
timekeeping_update_from_shadow(aux_tkd, TK_UPDATE_ALL);
return 0;
diff --git a/kernel/time/vsyscall.c b/kernel/time/vsyscall.c
index 8ba8b0d..aa59919 100644
--- a/kernel/time/vsyscall.c
+++ b/kernel/time/vsyscall.c
@@ -159,10 +159,10 @@ void vdso_time_update_aux(struct timekeeper *tk)
if (clock_mode != VDSO_CLOCKMODE_NONE) {
fill_clock_configuration(vc, &tk->tkr_mono);
- vdso_ts->sec = tk->xtime_sec;
+ vdso_ts->sec = tk->xtime_sec + tk->monotonic_to_aux.tv_sec;
nsec = tk->tkr_mono.xtime_nsec >> tk->tkr_mono.shift;
- nsec += tk->offs_aux;
+ nsec += tk->monotonic_to_aux.tv_nsec;
vdso_ts->sec += __iter_div_u64_rem(nsec, NSEC_PER_SEC, &nsec);
nsec = nsec << tk->tkr_mono.shift;
vdso_ts->nsec = nsec;
Powered by blists - more mailing lists