From 762af5a2aa0ad18da1316666dae30d369268d44c Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Thomas=20Wei=C3=9Fschuh?= Date: Mon, 25 Aug 2025 15:26:35 +0200 Subject: vdso/vsyscall: Avoid slow division loop in auxiliary clock update MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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/ --- include/linux/timekeeper_internal.h | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h index c27aac67cb3f..b8ae89ea28ab 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; -- cgit v1.2.3