[Qemu-devel] guest: NO_HZ FULL will not work with unstable sched clock

[Stefan Priebe]

Hi,

while switching to a FULL tickless kernel i detected that all our VMs
produce the following stack trace while running under qemu 2.3.0.

[    0.195160] HPET: 3 timers in total, 0 timers will be used for
per-cpu timer
[    0.195181] hpet0: at MMIO 0xfed00000, IRQs 2, 8, 0
[    0.195188] hpet0: 3 comparators, 64-bit 100.000000 MHz counter
[    0.200119] Switched to clocksource hpet
[    0.201164] ------------[ cut here ]------------
[    0.201193] WARNING: CPU: 1 PID: 1 at kernel/time/tick-sched.c:192
can_stop_full_tick+0x1c1/0x200()
[    0.201199] NO_HZ FULL will not work with unstable sched clock
[    0.201203] Modules linked in:
[    0.201214] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 3.18.20+55-ph #1
[    0.201219] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS rel-1.8.1-0-g4adadbd-20150316_085822-nilsson.home.kraxel.org 04/01/2014
[    0.201226]  0000000000000009 ffff88023fc43e88 ffffffff815f5889
00000000000008df
[    0.201230]  ffff88023fc43ed8 ffff88023fc43ec8 ffffffff8107433c
ffff88023fc43ea8
[    0.201233]  0000000000000000 0000000000000001 ffff880236c41300
00000000cbbde78b
[    0.201237] Call Trace:
[    0.201240]  <IRQ>  [<ffffffff815f5889>] dump_stack+0x46/0x58
[    0.201260]  [<ffffffff8107433c>] warn_slowpath_common+0x8c/0xc0
[    0.201264]  [<ffffffff81074426>] warn_slowpath_fmt+0x46/0x50
[    0.201270]  [<ffffffff810ddc31>] can_stop_full_tick+0x1c1/0x200
[    0.201274]  [<ffffffff810ddfc7>] tick_nohz_irq_exit+0x97/0xd0
[    0.201277]  [<ffffffff81077f0d>] irq_exit+0xcd/0x130
[    0.201286]  [<ffffffff8103419a>] smp_apic_timer_interrupt+0x4a/0x60
[    0.201293]  [<ffffffff815fc4ea>] apic_timer_interrupt+0x6a/0x70
[    0.201296]  <EOI>  [<ffffffff811bc1d5>] ? __d_lookup+0x55/0x160
[    0.201309]  [<ffffffff811bc315>] d_lookup+0x35/0x60
[    0.201312]  [<ffffffff811adc1b>] lookup_dcache+0x3b/0xd0
[    0.201315]  [<ffffffff811adcd3>] __lookup_hash+0x23/0x50
[    0.201319]  [<ffffffff811aeaae>] lookup_one_len+0xce/0x120
[    0.201328]  [<ffffffff812d062f>] __create_file+0x8f/0x260
[    0.201332]  [<ffffffff812d089b>] debugfs_create_dir+0x1b/0x20
[    0.201338]  [<ffffffff8111d9a8>] event_create_dir+0x68/0x520
[    0.201342]  [<ffffffff81d5bdb0>] event_trace_init+0x188/0x210
[    0.201348]  [<ffffffff81113e1b>] ? trace_create_file+0x1b/0x50
[    0.201352]  [<ffffffff81d5bc28>] ? event_trace_enable+0x1a2/0x1a2
[    0.201359]  [<ffffffff81000328>] do_one_initcall+0xd8/0x200
[    0.201368]  [<ffffffff81090200>] ? parse_args+0x1f0/0x470
[    0.201373]  [<ffffffff810b1c33>] ? __wake_up+0x53/0x70
[    0.201378]  [<ffffffff81d3e1ce>] kernel_init_freeable+0x168/0x1ff
[    0.201381]  [<ffffffff81d3d917>] ? do_early_param+0x8c/0x8c
[    0.201389]  [<ffffffff812f0680>] ? cryptomgr_probe+0x60/0xe0
[    0.201398]  [<ffffffff815e6f30>] ? rest_init+0x80/0x80
[    0.201401]  [<ffffffff815e6f3e>] kernel_init+0xe/0xf0
[    0.201405]  [<ffffffff815fb708>] ret_from_fork+0x58/0x90
[    0.201408]  [<ffffffff815e6f30>] ? rest_init+0x80/0x80
[    0.201415] ---[ end trace a15ba3bc1d247b4c ]---

Stefan