This is a note to let you know that I've just added the patch titled tick/common: Align tick period with the HZ tick. to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: tick-common-align-tick-period-with-the-hz-tick.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 82261dd5f85d6e27ecc8b79e51ea39de0e30ee54 Author: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Date: Tue Apr 18 14:26:39 2023 +0200 tick/common: Align tick period with the HZ tick. [ Upstream commit e9523a0d81899361214d118ad60ef76f0e92f71d ] With HIGHRES enabled tick_sched_timer() is programmed every jiffy to expire the timer_list timers. This timer is programmed accurate in respect to CLOCK_MONOTONIC so that 0 seconds and nanoseconds is the first tick and the next one is 1000/CONFIG_HZ ms later. For HZ=250 it is every 4 ms and so based on the current time the next tick can be computed. This accuracy broke since the commit mentioned below because the jiffy based clocksource is initialized with higher accuracy in read_persistent_wall_and_boot_offset(). This higher accuracy is inherited during the setup in tick_setup_device(). The timer still fires every 4ms with HZ=250 but timer is no longer aligned with CLOCK_MONOTONIC with 0 as it origin but has an offset in the us/ns part of the timestamp. The offset differs with every boot and makes it impossible for user land to align with the tick. Align the tick period with CLOCK_MONOTONIC ensuring that it is always a multiple of 1000/CONFIG_HZ ms. Fixes: 857baa87b6422 ("sched/clock: Enable sched clock early") Reported-by: Gusenleitner Klaus <gus@xxxxxxxx> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Link: https://lore.kernel.org/20230406095735.0_14edn3@xxxxxxxxxxxxx Link: https://lore.kernel.org/r/20230418122639.ikgfvu3f@xxxxxxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 46789356f856e..65b8658da829e 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -218,9 +218,19 @@ static void tick_setup_device(struct tick_device *td, * this cpu: */ if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) { + ktime_t next_p; + u32 rem; + tick_do_timer_cpu = cpu; - tick_next_period = ktime_get(); + next_p = ktime_get(); + div_u64_rem(next_p, TICK_NSEC, &rem); + if (rem) { + next_p -= rem; + next_p += TICK_NSEC; + } + + tick_next_period = next_p; #ifdef CONFIG_NO_HZ_FULL /* * The boot CPU may be nohz_full, in which case set