Warning: NO_HZ FULL will not work with unstable sched clock

Warning: NO_HZ FULL will not work with unstable sched clock

[Alexander Beregalov]

Hi,
It first appeared some time after 3.9 or 3.10 and still persist.
I guess bisect is not required?

WARNING: CPU: 1 PID: 6 at kernel/time/tick-sched.c:187
can_stop_full_tick+0x8d/0x9a()
NO_HZ FULL will not work with unstable sched clock
Modules linked in:

CPU: 1 PID: 6 Comm: kworker/u8:0 Not tainted 3.12.0-01714-ga1212d2 #1
Hardware name:                  /D525MW, BIOS
MWPNT10N.86A.0084.2011.0726.1300 07/26/2011
 00000000000000bb ffff8800bea83e88 ffffffff813ba3b0 0000000000000050
 ffff8800bea83ed8 ffff8800bea83ec8 ffffffff81031441 ffff8800bb07a170
 ffffffff810687db 0000000000000000 0000000000000001 ffff8800bea91ac0
Call Trace:
 <IRQ>  [<ffffffff813ba3b0>] dump_stack+0x46/0x58
 [<ffffffff81031441>] warn_slowpath_common+0x78/0x92
 [<ffffffff810687db>] ? can_stop_full_tick+0x8d/0x9a
 [<ffffffff810314f1>] warn_slowpath_fmt+0x42/0x44
 [<ffffffff81052353>] ? account_system_time+0x114/0x15c
 [<ffffffff810687db>] can_stop_full_tick+0x8d/0x9a
 [<ffffffff810689ef>] tick_nohz_irq_exit+0x77/0x93
 [<ffffffff81034c28>] irq_exit+0xd3/0xdc
 [<ffffffff81021b7c>] smp_apic_timer_interrupt+0x40/0x4d
 [<ffffffff813c474a>] apic_timer_interrupt+0x6a/0x70
 <EOI>  [<ffffffff8104da85>] ? finish_task_switch+0x6f/0xd1
 [<ffffffff8104da5a>] ? finish_task_switch+0x44/0xd1
 [<ffffffff813bd0ae>] __schedule+0x75a/0x7f3
 [<ffffffff813be291>] ? _raw_spin_unlock_irqrestore+0x9/0xb
 [<ffffffff8104d704>] ? complete+0x43/0x4b
 [<ffffffff8104068c>] ? umh_complete+0x17/0x20
 [<ffffffff81040710>] ? __call_usermodehelper+0x7b/0x80
 [<ffffffff81042b96>] ? process_one_work+0x2f4/0x304
 [<ffffffff813bd3f6>] schedule+0x5f/0x61
 [<ffffffff810433ba>] worker_thread+0x2a8/0x2ad
 [<ffffffff81043112>] ? manage_workers.isra.31+0x1b9/0x1b9
 [<ffffffff81047b86>] kthread+0xb6/0xbe
 [<ffffffff81047ad0>] ? __kthread_parkme+0x68/0x68
 [<ffffffff813c39fc>] ret_from_fork+0x7c/0xb0
 [<ffffffff81047ad0>] ? __kthread_parkme+0x68/0x68

Re: Warning: NO_HZ FULL will not work with unstable sched clock

[Frederic Weisbecker]

On Sat, Nov 09, 2013 at 12:32:06PM +0400, Alexander Beregalov wrote:
> Hi,
> It first appeared some time after 3.9 or 3.10 and still persist.
> I guess bisect is not required?
> 
> WARNING: CPU: 1 PID: 6 at kernel/time/tick-sched.c:187
> can_stop_full_tick+0x8d/0x9a()
> NO_HZ FULL will not work with unstable sched clock

Right, it's not a bug, just a warning we've put to make sure that users of
full dynticks are aware of limitations when the sched clock is unstable.

That's something we want to fix in the long run as it seems that quite
a lot of people have unstable tsc.

Thanks.