Re: [Xen-devel] vpmu=1 and running 'perf top' within a PVHVM guest eventually hangs dom0 and hypervisor has stuck vCPUS. Romley-EP (model=45, stepping=2)

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.03.13 at 21:54, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:
> On 03/12/2013 04:31 PM, Konrad Rzeszutek Wilk wrote:
>> On Tue, Mar 12, 2013 at 02:50:59PM -0400, Boris Ostrovsky wrote:
>>> On 03/12/2013 01:30 PM, Konrad Rzeszutek Wilk wrote:
>>>> This issue I am encountering seems to only happen on multi-socket
>>>> machines.
>>> I believe I was able to reproduce this (once) on my laptop.
>>>
>>>> It also does not help that the only multi-socket box I have is
>>>> an Romley-EP (so two socket SandyBridge CPUs). The other
>>>> SandyBridge boxes I've (one socket) are not showing this. Granted
>>>> they are also a different model (42).
>>>>
>>>> The problem is that when I run 'perf top' within an SMP PVHVM
>>>> guest, after a couple of seconds or minutes the guest hangs.
>>>> Hypervisor ends up stuck too looping, and then the dom0 ends
>>>> up hanging as well.
>>>>
>>>> Dumping the cpu registers (Ctrl-A x3, then 'd'
>>>> shows that the guest is pretty firmly stuck in vmx_vmexit_handler:
>>>>
>>>> (XEN)    [<ffff82c4c01d386f>] vmx_vmexit_handler+0x22f/0x174
>>> And in my case this address is the second instruction after STI, i.e. we
>>> are right at the point where interrupts got enabled.
>>>
>>> So I am wondering whether this has something to do with the counter
>>> overflow interrupt (which I believe is an NMI).
>> Interestingly enough, if I run the PVHVM guest with 'nowatchdog'
>> it runs fine!
> 
> I think by default perf top runs off timer interrupt so it does not use 
> HW counters. But watchdog
> is implemented on top of the counters so perhaps it fires the interrupt 
> at a bad time, messing
> something up.

Or perhaps simply at too high a rate?

Jan


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