linux/kernel/time/timekeeping.c, branch v6.17

vdso/vsyscall: Avoid slow division loop in auxiliary clock update

2025-09-03T09:55:11Z

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 Signed-off-by: Thomas Weißschuh Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/all/20250825-vdso-auxclock-division-v1-1-a1d32a16a313@linutronix.de Closes: https://lore.kernel.org/lkml/aKwsNNWsHJg8IKzj@localhost/

Merge tag 'timers-ptp-2025-07-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2025-07-29T21:12:52Z

Pull timekeeping and VDSO updates from Thomas Gleixner: - Introduce support for auxiliary timekeepers PTP clocks can be disconnected from the universal CLOCK_TAI reality for various reasons including regularatory requirements for functional safety redundancy. The kernel so far only supports a single notion of time, which means that all clocks are correlated in frequency and only differ by offset to each other. Access to non-correlated PTP clocks has been available so far only through the file descriptor based "POSIX clock IDs", which are subject to locking and have to go all the way out to the hardware. The access is not only horribly slow, as it has to go all the way out to the NIC/PTP hardware, but that also prevents the kernel to read the time of such clocks e.g. from the network stack, where it is required for TSN networking both on the transmit and receive side unless the hardware provides offloading. The auxiliary clocks provide a mechanism to support arbitrary clocks which are not correlated to the system clock. This is not restricted to the PTP use case on purpose as there is no kernel side association of these clocks to a particular PTP device because that's a pure user space configuration decision. Having them independent allows to utilize them for other purposes and also enables them to be tested without hardware dependencies. To avoid pointless overhead these clocks have to be enabled individualy via a new sysfs interface to reduce the overhead to a single compare in the hotpath if they are enabled at the Kconfig level at all. These clocks utilize the existing timekeeping/NTP infrastructures, which has been made possible over the recent releases by incrementaly converting these infrastructures over from a single static instance to a multi-instance pointer based implementation without any performance regression reported. The auxiliary clocks provide the same "emulation" of a "correct" clock as the existing CLOCK_* variants do with an independent instance of data and provide the same steering mechanism through the existing sys_clock_adjtime() interface, which has been confirmed to work by the chronyd(8) maintainer. That allows to provide lockless kernel internal and VDSO support so that applications and kernel internal functionalities can access these clocks without restrictions and at the same performance as the existing system clocks. - Avoid double notifications in the adjtimex() syscall. Not a big issue, but a trivial to avoid latency source. * tag 'timers-ptp-2025-07-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (39 commits) vdso/gettimeofday: Add support for auxiliary clocks vdso/vsyscall: Update auxiliary clock data in the datapage vdso: Introduce aux_clock_resolution_ns() vdso/gettimeofday: Introduce vdso_get_timestamp() vdso/gettimeofday: Introduce vdso_set_timespec() vdso/gettimeofday: Introduce vdso_clockid_valid() vdso/gettimeofday: Return bool from clock_gettime() helpers vdso/gettimeofday: Return bool from clock_getres() helpers vdso/helpers: Add helpers for seqlocks of single vdso_clock vdso/vsyscall: Split up __arch_update_vsyscall() into __arch_update_vdso_clock() vdso/vsyscall: Introduce a helper to fill clock configurations timekeeping: Remove the temporary CLOCK_AUX workaround timekeeping: Provide ktime_get_clock_ts64() timekeeping: Provide interface to control auxiliary clocks timekeeping: Provide update for auxiliary timekeepers timekeeping: Provide adjtimex() for auxiliary clocks timekeeping: Prepare do_adtimex() for auxiliary clocks timekeeping: Make do_adjtimex() reusable timekeeping: Add auxiliary clock support to __timekeeping_inject_offset() timekeeping: Make timekeeping_inject_offset() reusable ...

timekeeping: Zero initialize system_counterval when querying time from phc drivers

2025-07-22T12:25:21Z

Most drivers only populate the fields cycles and cs_id of system_counterval in their get_time_fn() callback for get_device_system_crosststamp(), unless they explicitly provide nanosecond values. When the use_nsecs field was added to struct system_counterval, most drivers did not care. Clock sources other than CSID_GENERIC could then get converted in convert_base_to_cs() based on an uninitialized use_nsecs field, which usually results in -EINVAL during the following range check. Pass in a fully zero initialized system_counterval_t to cure that. Fixes: 6b2e29977518 ("timekeeping: Provide infrastructure for converting to/from a base clock") Signed-off-by: Markus Blöchl Signed-off-by: Thomas Gleixner Acked-by: John Stultz Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/20250720-timekeeping_uninit_crossts-v2-1-f513c885b7c2@blochl.de

vdso/vsyscall: Update auxiliary clock data in the datapage

2025-07-18T11:45:33Z

Expose the auxiliary clock data so it can be read from the vDSO. Architectures not using the generic vDSO time framework, namely SPARC64, are not supported. Signed-off-by: Thomas Weißschuh Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/all/20250701-vdso-auxclock-v1-11-df7d9f87b9b8@linutronix.de

vdso: Introduce aux_clock_resolution_ns()

2025-07-18T11:45:32Z

Move the constant resolution to a shared header, so the vDSO can use it and return it without going through a syscall. Signed-off-by: Thomas Weißschuh Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/all/20250701-vdso-auxclock-v1-10-df7d9f87b9b8@linutronix.de

Merge tag 'ktime-get-clock-ts64-for-ptp' into timers/ptp

2025-07-03T12:35:53Z

Pull the base implementation of ktime_get_clock_ts64() for PTP, which contains a temporary CLOCK_AUX* workaround. That was created to allow integration of depending changes into the networking tree. The workaround is going to be removed in a subsequent change in the timekeeping tree. Signed-off-by: Thomas Gleixner

timekeeping: Provide ktime_get_clock_ts64()

2025-07-03T12:18:06Z

PTP implements an inline switch case for taking timestamps from various POSIX clock IDs, which already consumes quite some text space. Expanding it for auxiliary clocks really becomes too big for inlining. Provide a out of line version. The function invalidates the timestamp in case the clock is invalid. The invalidation allows to implement a validation check without the need to propagate a return value through deep existing call chains. Due to merge logistics this temporarily defines CLOCK_AUX[_LAST] if undefined, so that the plain branch, which does not contain any of the core timekeeper changes, can be pulled into the networking tree as prerequisite for the PTP side changes. These temporary defines are removed after that branch is merged into the tip::timers/ptp branch. That way the result in -next or upstream in the next merge window has zero dependencies. Signed-off-by: Thomas Gleixner Reviewed-by: Vadim Fedorenko Acked-by: John Stultz Link: https://lore.kernel.org/all/20250701132628.357686408@linutronix.de

timekeeping: Provide interface to control auxiliary clocks

2025-06-27T18:13:13Z

Auxiliary clocks are disabled by default and attempts to access them fail. Provide an interface to enable/disable them at run-time. Signed-off-by: Thomas Gleixner Acked-by: John Stultz Link: https://lore.kernel.org/all/20250625183758.444626478@linutronix.de

timekeeping: Provide update for auxiliary timekeepers

2025-06-27T18:13:13Z

Update the auxiliary timekeepers periodically. For now this is tied to the system timekeeper update from the tick. This might be revisited and moved out of the tick. Signed-off-by: Thomas Gleixner Acked-by: John Stultz Link: https://lore.kernel.org/all/20250625183758.382451331@linutronix.de

timekeeping: Provide adjtimex() for auxiliary clocks

2025-06-27T18:13:13Z

The behaviour is close to clock_adtime(CLOCK_REALTIME) with the following differences: 1) ADJ_SETOFFSET adjusts the auxiliary clock offset 2) ADJ_TAI is not supported 3) Leap seconds are not supported 4) PPS is not supported Signed-off-by: Thomas Gleixner Acked-by: John Stultz Link: https://lore.kernel.org/all/20250625183758.317946543@linutronix.de