linux/kernel/time, branch v6.17

hrtimers: Unconditionally update target CPU base after offline timer migration

2025-09-09T12:05:16Z

When testing softirq based hrtimers on an ARM32 board, with high resolution mode and NOHZ inactive, softirq based hrtimers fail to expire after being moved away from an offline CPU: CPU0 CPU1 hrtimer_start(..., HRTIMER_MODE_SOFT); cpu_down(CPU1) ... hrtimers_cpu_dying() // Migrate timers to CPU0 smp_call_function_single(CPU0, returgger_next_event); retrigger_next_event() if (!highres && !nohz) return; As retrigger_next_event() is a NOOP when both high resolution timers and NOHZ are inactive CPU0's hrtimer_cpu_base::softirq_expires_next is not updated and the migrated softirq timers never expire unless there is a softirq based hrtimer queued on CPU0 later. Fix this by removing the hrtimer_hres_active() and tick_nohz_active() check in retrigger_next_event(), which enforces a full update of the CPU base. As this is not a fast path the extra cost does not matter. [ tglx: Massaged change log ] Fixes: 5c0930ccaad5 ("hrtimers: Push pending hrtimers away from outgoing CPU earlier") Co-developed-by: Frederic Weisbecker Signed-off-by: Frederic Weisbecker Signed-off-by: Xiongfeng Wang Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/all/20250805081025.54235-1-wangxiongfeng2@huawei.com

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 'bitmap-for-6.17' of https://github.com/norov/linux

2025-07-31T23:52:32Z

Pull bitmap updates from Yury Norov: - find_random_bit() series (Yury) - GENMASK() consolidation (Vincent) - random cleanups (Shaopeng, Ben, Yury) * tag 'bitmap-for-6.17' of https://github.com/norov/linux: bitfield: Ensure the return values of helper functions are checked test_bits: add tests for __GENMASK() and __GENMASK_ULL() bits: unify the non-asm GENMASK*() bits: split the definition of the asm and non-asm GENMASK*() cpumask: Remove unnecessary cpumask_nth_andnot() watchdog: fix opencoded cpumask_next_wrap() in watchdog_next_cpu() clocksource: Improve randomness in clocksource_verify_choose_cpus() cpumask: introduce cpumask_random() bitmap: generalize node_random()

clocksource: Improve randomness in clocksource_verify_choose_cpus()

2025-07-31T15:27:48Z

The current algorithm of picking a random CPU works OK for dense online cpumask, but if cpumask is non-dense, the distribution of picked CPUs is skewed. For example, on 8-CPU board with CPUs 4-7 offlined, the probability of selecting CPU 0 is 5/8. Accordingly, cpus 1, 2 and 3 are chosen with probability 1/8 each. The proper algorithm should pick each online CPU with probability 1/4. Switch it to cpumask_random(), which has better statistical characteristics. CC: Andrew Morton Acked-by: John Stultz Reviewed-by: Thomas Gleixner Signed-off-by: "Yury Norov [NVIDIA]"

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 ...

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

2025-07-29T21:08:21Z

Pull timer core updates from Thomas Gleixner: - Simplify the logic in the timer migration code - Simplify the clocksource code by utilizing the more modern cpumask+*() interfaces * tag 'timers-core-2025-07-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: clocksource: Use cpumask_next_wrap() in clocksource_watchdog() clocksource: Use cpumask_any_but() in clocksource_verify_choose_cpus() timers/migration: Clean up the loop in tmigr_quick_check()

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

2025-07-29T21:02:53Z

Pull timer cleanups from Thomas Gleixner: "A treewide cleanup of struct cycle_counter const annotations. The initial idea of making them const was correct as they were seperate instances. When they got embedded into larger data structures, which are even modified by the callback this got moot. The only reason why this went unnoticed is that the required container_of() casts the const attribute forcefully away. Stop pretending that it is const" * tag 'timers-cleanups-2025-07-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: time/timecounter: Fix the lie that struct cyclecounter is const

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