kvm guest hangs [was Re: Xen Dom0 [was Re: Announcing Fedora 11 Alpha (blink)]]

Mark McLoughlin markmc at redhat.com
Fri Feb 6 10:22:59 UTC 2009

(Please respect my Reply-to:)

On Fri, 2009-02-06 at 19:10 +0900, John Summerfield wrote:
> Mark McLoughlin wrote:
> > On Fri, 2009-02-06 at 18:55 +0900, John Summerfield wrote:
> >> Mark McLoughlin wrote:
> >>
> >>> Try booting the guest with clocksource=acpi_pm on the kernel command
> >>> line. If that helps, it's this bug:
> >>>
> >>>   https://bugzilla.redhat.com/475598
> >>>
> >>> It's an issue with KVM's paravirt clock. We have a workaround in the
> >>> rawhide host kernel which disables kvmclock support on affected hosts. A
> >>> real fix is in progress upstream.
> >>>
> >>> The F-10 branch has the workaround, but only for the 2.6.29 builds. I
> >>> don't think we have it in the 2.6.27 updates (i.e. the
> >>> private-fedora-10-2_6_27 branch).
> >>>
> >>> Chuck, could we get linux-2.6-kvmclock-unsync-tsc-workaround.patch
> >>> pulled into F-10?
> >> I'm fully virtualised. I think. What's this about a paravirt clock in KVM?
> > 
> > KVM uses hardware virtualization support to run guests, yes, but it also
> > allows guests to use paravirtualization for some performance critical
> > operations - so e.g. pv block/network drivers, pv clock and pv MMU.
> My debian guest uses tsc for its clock source (I just looked under sys, 
> having read that bug report and got a clue). It has none of the pv stuff.

Ah, I missed that.

> I've also had problems installing CentOS 5.x guests, I don't think I've 
> managed it yet.
> I didn't report it because I don't like "it doesn't work" reports, and 
> really I had no more than that.

Well, we'd definitely prefer to have the report and work with you to get
more info.

We've also got this page for giving hints on what information is useful:



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