Re: [PATCH] sched/cputime: Don't warn when the tick period starts after idle exit

[Breno Leitao <leitao@debian.org>]

On Sun, Oct 25, 2026 at 11:02:02AM +0100, Stian Halseth wrote:
> I could not hit the window in a KVM guest, but instrumented, the guest
> showed the sched timer armed 5.9 ms after now at HZ=250 right after a
> jiffies -> hpet switch, and tick stops saving a ts->last_tick more than
> a tick ahead. The fix boots without warnings there.

I am seeing this on my testing real hosts:

           clocksource: Switched to clocksource tsc-early
           ------------[ cut here ]------------
           WARNING: kernel/sched/cputime.c:481 at kcpustat_dyntick_stop+0x15e/0x1d0, CPU#2: swapper/2/0  [warn]
           Modules linked in:
           CPU: 2 UID: 0 PID: 0 Comm: swapper/2 Tainted: G S                   7.3.0-0_fbk701_debugnightly_rc0_upstream_17997_gc339f4010dea #1 PREEMPTLAZ
           Tainted: [S]=CPU_OUT_OF_SPEC
           Hardware name: Quanta Twin Lakes MP/Twin Lakes Passive MP, BIOS F09_3A23 12/08/2020
           RIP: 0010:kcpustat_dyntick_stop+0x15e/0x1d0
           Code: de e8 96 00 00 00 42 0f b6 44 2d 00 84 c0 75 4d 41 c6 07 00 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d c3 0f 0b e9 2e ff ff ff <0f> 0b eb
           RSP: 0000:ffff88828a22fe38 EFLAGS: 00010087
           RAX: 0000000b9aef1500 RBX: 0000000b9aeb7036 RCX: 0000000000000001
           RDX: 00092e9200000000 RSI: ffffffff851ec9c0 RDI: ffffffff851ccaa0
           RBP: 1ffff111c3e65a3b R08: ffffffff8152bd65 R09: 0000000000000001
           R10: dffffc0000000000 R11: fffffbfff0f78a9a R12: fffffffffffc5b36
           R13: dffffc0000000000 R14: 0000000b9aef1500 R15: ffff888e1f32d1d8
           FS:  0000000000000000(0000) GS:ffff888e9684e000(0000) knlGS:0000000000000000
           CR2: 0000000000000000 CR3: 000000107162a001 CR4: 00000000007706f0
           PKRU: 55555554
           Call Trace:
           <TASK>
           tick_nohz_idle_exit+0x1d5/0x2d0
           do_idle+0x3b7/0x4a0
           cpu_startup_entry+0x45/0x60
           start_secondary+0x1b3/0x200
           common_startup_64+0x13e/0x140
           </TASK>
           irq event stamp: 406130
           hardirqs last  enabled at (406129): [<ffffffff849e90cf>] cpuidle_enter_state+0x13f/0x465
           hardirqs last disabled at (406130): [<ffffffff81557bc2>] tick_nohz_idle_exit+0x62/0x2d0
           softirqs last  enabled at (406118): [<ffffffff8126dc76>] __irq_exit_rcu+0xc6/0x230
           softirqs last disabled at (406111): [<ffffffff8126dc76>] __irq_exit_rcu+0xc6/0x230
           ---[ end trace 0000000000000000 ]---