bhyve: centos 7.1 with multiple virtual processors

[Neel Natu]

Hi Andriy,

FWIW I can boot up a Centos 7.1 virtual machine with 2 and 4 vcpus
fine on my host with 8 physical cores.

I have some questions about your setup inline.

On Mon, Jun 22, 2015 at 4:14 AM, Andriy Gapon <avg at freebsd.org> wrote:
>
> If I run a CentOS 7.1 VM with more than one CPU more often than not it would
> hang on startup and bhyve would start spinning.
>
> The following are the last messages seen in the VM:
>
> Switching to clocksource hpet
> ------------[ cut here ]------------
> WARNING: at kernel/time/clockevents.c:239 clockevents_program_event+0xdb/0xf0()
> Modules linked in:
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.10.0-229.4.2.el7.x86_64 #1
> Hardware name:   BHYVE, BIOS 1.00 03/14/2014
>  0000000000000000 00000000cab5bdb6 ffff88003fc03e08 ffffffff81604eaa
>  ffff88003fc03e40 ffffffff8106e34b 80000000000f423f 80000000000f423f
>  ffffffff81915440 0000000000000000 0000000000000000 ffff88003fc03e50
> Call Trace:
>  <IRQ>  [<ffffffff81604eaa>] dump_stack+0x19/0x1b
>  [<ffffffff8106e34b>] warn_slowpath_common+0x6b/0xb0
>  [<ffffffff8106e49a>] warn_slowpath_null+0x1a/0x20
>  [<ffffffff810ce6eb>] clockevents_program_event+0xdb/0xf0
>  [<ffffffff810cf211>] tick_handle_periodic_broadcast+0x41/0x50
>  [<ffffffff81016525>] timer_interrupt+0x15/0x20
>  [<ffffffff8110b5ee>] handle_irq_event_percpu+0x3e/0x1e0
>  [<ffffffff8110b7cd>] handle_irq_event+0x3d/0x60
>  [<ffffffff8110e467>] handle_edge_irq+0x77/0x130
>  [<ffffffff81015cff>] handle_irq+0xbf/0x150
>  [<ffffffff81077df7>] ? irq_enter+0x17/0xa0
>  [<ffffffff816172af>] do_IRQ+0x4f/0xf0
>  [<ffffffff8160c4ad>] common_interrupt+0x6d/0x6d
>  <EOI>  [<ffffffff8126e359>] ? selinux_inode_alloc_security+0x59/0xa0
>  [<ffffffff811de58f>] ? __d_instantiate+0xbf/0x100
>  [<ffffffff811de56f>] ? __d_instantiate+0x9f/0x100
>  [<ffffffff811de60d>] d_instantiate+0x3d/0x70
>  [<ffffffff8124d748>] debugfs_mknod.isra.5.part.6.constprop.15+0x98/0x130
>  [<ffffffff8124da82>] __create_file+0x1c2/0x2c0
>  [<ffffffff81a6c6bf>] ? set_graph_function+0x1f/0x1f
>  [<ffffffff8124dbcb>] debugfs_create_dir+0x1b/0x20
>  [<ffffffff8112c1ce>] tracing_init_dentry_tr+0x7e/0x90
>  [<ffffffff8112c250>] tracing_init_dentry+0x10/0x20
>  [<ffffffff81a6c6d2>] ftrace_init_debugfs+0x13/0x1fd
>  [<ffffffff81a6c6bf>] ? set_graph_function+0x1f/0x1f
>  [<ffffffff810020e8>] do_one_initcall+0xb8/0x230
>  [<ffffffff81a45203>] kernel_init_freeable+0x18b/0x22a
>  [<ffffffff81a449db>] ? initcall_blacklist+0xb0/0xb0
>  [<ffffffff815f33f0>] ? rest_init+0x80/0x80
>  [<ffffffff815f33fe>] kernel_init+0xe/0xf0
>  [<ffffffff81614d3c>] ret_from_fork+0x7c/0xb0
>  [<ffffffff815f33f0>] ? rest_init+0x80/0x80
> ---[ end trace d5caa1cab8e7e98d ]---
>

A few questions to narrow this down:
- Is the host very busy when the VM is started (or what is the host
doing when this happened)?
- How many vcpus are you giving to the VM?
- How many cores on the host?

>
> At the same time sometimes there is one or more of spurious NMIs on the _host_
> system:
> NMI ISA c, EISA ff
> NMI ... going to debugger
>

Hmm, that's interesting. Are you using hwpmc to do instruction sampling?

> bhyve seems to spin here:
> vmm.ko`svm_vmrun+0x894
> vmm.ko`vm_run+0xbb7
> vmm.ko`vmmdev_ioctl+0x5a4
> kernel`devfs_ioctl_f+0x13b
> kernel`kern_ioctl+0x1e1
> kernel`sys_ioctl+0x16a
> kernel`amd64_syscall+0x3ca
> kernel`0xffffffff8088997b
>
> (kgdb) list *svm_vmrun+0x894
> 0xffffffff813c9194 is in svm_vmrun
> (/usr/src/sys/modules/vmm/../../amd64/vmm/amd/svm.c:1895).
> 1890
> 1891    static __inline void
> 1892    enable_gintr(void)
> 1893    {
> 1894
> 1895            __asm __volatile("stgi");
> 1896    }
> 1897
> 1898    /*
> 1899     * Start vcpu with specified RIP.
>

Yeah, that's not surprising because host interrupts are blocked when
the cpu is executing in guest context. The 'enable_gintr()' enables
interrupts so it gets blamed by the interrupt-based sampling.

In this case it just means that the cpu was in guest context when a
host-interrupt fired.

best
Neel

> --
> Andriy Gapon
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