/sys/kernel/debug/tracing # echo mmiotrace > current_tracer 
[  106.528373] mmiotrace: Disabling non-boot CPUs...
[  106.546027] Unregister pv shared memory for cpu 1
[  106.550758] ------------[ cut here ]------------
[  106.551354] IRQs not enabled as expected
[  106.551785] WARNING: CPU: 1 PID: 0 at /home/mhiramat/ksrc/linux/kernel/time/tick-sched.c:982 tick_nohz_idle_enter+0x99/0xb0
[  106.552964] Modules linked in:
[  106.553299] CPU: 1 PID: 0 Comm: swapper/1 Tainted: G        W         4.18.0-rc6+ #15
[  106.554129] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1.fc26 04/01/2014
[  106.555058] RIP: 0010:tick_nohz_idle_enter+0x99/0xb0
[  106.555608] Code: 00 00 5b c3 8b 80 48 08 00 00 85 c0 75 a6 80 3d 59 8d 01 01 00 75 9d 48 c7 c7 9b 8f dc 81 c6 05 49 8d 01 01 01 e8 f7 4d f6 ff <0f> 0b eb 86 0f 0b eb ae 0f 1f 44 00 00 66 2e 0f 1f 84 00 00 00 00 
[  106.557796] RSP: 0018:ffffc9000013bec8 EFLAGS: 00010286
[  106.558307] RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000000
[  106.558997] RDX: 0000000000000002 RSI: 0000000000000001 RDI: 0000000000000001
[  106.559680] RBP: ffff88001f27c140 R08: 0000000000000000 R09: 0000000000000000
[  106.560374] R10: ffffc9000013bda8 R11: a8b925c7f0ce6f64 R12: 0000000000000000
[  106.561072] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[  106.561785] FS:  0000000000000000(0000) GS:ffff88001f640000(0000) knlGS:0000000000000000
[  106.562590] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  106.563141] CR2: 000000000045d6a0 CR3: 000000000201e000 CR4: 00000000000006a0
[  106.563821] Call Trace:
[  106.564074]  do_idle+0x3b/0x250
[  106.564384]  cpu_startup_entry+0x6f/0x80
[  106.564768]  start_secondary+0x1a2/0x1d0
[  106.565153]  secondary_startup_64+0xa5/0xb0
[  106.565568] irq event stamp: 4848732
[  106.565922] hardirqs last  enabled at (4848731): [<0000000000000000>]           (null)
[  106.566679] hardirqs last disabled at (4848732): [<0000000000000000>]           (null)
[  106.567441] softirqs last  enabled at (4848726): [<ffffffff810626bd>] irq_enter+0x5d/0x60
[  106.568224] softirqs last disabled at (4848725): [<ffffffff810626a2>] irq_enter+0x42/0x60
[  106.569004] ---[ end trace 574d547106ecd2dc ]---
[  106.569557] smpboot: CPU 1 is now offline
[  106.571199] mmiotrace: CPU1 is down.
[  106.582201] Unregister pv shared memory for cpu 2
[  106.584933] smpboot: CPU 2 is now offline
[  106.586182] mmiotrace: CPU2 is down.
[  106.597164] Unregister pv shared memory for cpu 3
[  106.599613] smpboot: CPU 3 is now offline
[  106.600605] mmiotrace: CPU3 is down.
[  106.610152] Unregister pv shared memory for cpu 4
[  106.612392] smpboot: CPU 4 is now offline
[  106.613499] mmiotrace: CPU4 is down.
[  106.628214] Unregister pv shared memory for cpu 5
[  106.631070] smpboot: CPU 5 is now offline
[  106.632484] mmiotrace: CPU5 is down.
[  106.644250] Unregister pv shared memory for cpu 6
[  106.647179] smpboot: CPU 6 is now offline
[  106.648693] mmiotrace: CPU6 is down.
[  106.654288] Unregister pv shared memory for cpu 7
[  106.657585] smpboot: CPU 7 is now offline
[  106.659339] mmiotrace: CPU7 is down.
[  106.660576] mmiotrace: enabled.