Re: soft lockup after stop/cont

[Carsten Otte <cotte-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>]

Dong, Eddie wrote:
> kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org wrote:
>> Jim Paris wrote:
>>> If I stop KVM in the monitor with "stop", wait a minute, and do
>>> "cont", a Linux guest gives me a "BUG: soft lockup detected on
>>> CPU#0". Is that expected behavior?
>> We have the same behavior on s390 when running in a virtual
>> environment. The issue is, that the guest physical cpu may be
>> scheduled away while a timer runs down. I don't think there's anything
>> kvm could do better regerding the soft lockup code. Soft lockup is
>> just broken for virtualized environments and needs to be fixed. For
>> the time being, just disable it in kconfig.
>>
> This is a well known issue, but we can fix by syncing TSC with PIT etc.
> But doing this we need to froze guest TSC when a VP is descheduled.
> 
> We enable this in Xen but feel it is too complicated so never wanna
> to do same thing in KVM per previous discussion. There are some
> side effect of course due to this.
> 
> In Xen some time you will see PV domain soft lockup, but never in 
> hardware HVM :-)  Hopefully Linux will have pv timer soon.
Yes, virtual timers will be the right fix for it. I believe Jan has a 
patch for that. Am I mistaken Jan? [adding Jan to CC:]

-------------------------------------------------------------------------
This SF.net email is sponsored by: Splunk Inc.
Still grepping through log files to find problems?  Stop.
Now Search log events and configuration files using AJAX and a browser.
Download your FREE copy of Splunk now >> http://get.splunk.com/