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Re: [libvirt] Fwd: How do you disable hpet in a kvm?



On 06/08/2010 03:59 PM, Richard W.M. Jones wrote:
Forwarding to libvir-list.

The KVM developers have been recommending that all guests use -no-hpet
flag.  Indeed, we've been adding this flag in libguestfs for quite a
long time.  However I notice that libvirt [in Rawhide] does not
include this flag for my guests.

-no-hpet isn't in the commandline by default, but can be added with the following bit of xml in the domain definition:

<clock>
<timer name='hpet' present='no'/>
</clock>

(if there is an existing <clock> section, you should add the "<timer name= ...>" to that, rather than creating a new one).

That functionality is in libvirt as of version 0.8.0.

Actually, I just realized while loking back through the code that the intent was for -no-hpet to be set if <timer name='hpet'/> is given with *no* "present" attribute (and if qemu supports it, of course), but that isn't being done, so I'm filing a bug for that. (the idea is that then the xml for all domains can just say "<timer name='hpet'/>" and the option will be added when qemu supports it, and it will be silently ignored when it doesn't support it.

Rich.

----- Forwarded message from "Frederick N. Brier"<fnbrier gmail com>  -----

Subject: [fedora-virt] How do you disable hpet in a kvm?
Date: Tue, 08 Jun 2010 14:15:06 -0400
To: virt lists fedoraproject org

I installed PBX In A Flash (PIAF) as a VM on a Fedora 11 64 bit host.
PIAF is a 32 bit CentOS 5.2 distro for running Asterisk.  I, like many
others, am getting the error message "rtc: lost some interrupts at 1024hz"
repeating over and over on the console.  Some people have apparently gotten
rid of this error message by disabling hpet in the BIOS.  However, this is
a VM (kvm).

I tried adding nohpet as a kernel parameter in /boot/grub/menu.lst, but
that effects the linux OS, not the BIOS.  It did not fix it.

I found references to a -no-hpet qemu parameter.  However, I cannot find
how to set it in a VM created using virt-manager and an ISO image.  In the
/etc/libvirt of the host I found XML configuration files describing the
VMs.  These appear to be the same as those created using the virsh dumpxml
command.  There does not appear to be an XML element as there is for acpi
and apic.  The man page describing the XML format does not have an HPET
related option.  I could not find an example or sample of it being disabled
in a libvirt XML file.  Nor does there appear to be a schema (xsd or dtd)
for the libvirt file format, which might have had an hpet element or
attribute.

Ideally, is there a way to disable HPET in the BIOS for a specific VM, and
not all VMs.  Thank you.

Fred
//

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