[fedora-virt] performance regressions in Fedora 13?

[Cole Robinson]

On 05/27/2010 11:33 AM, Kenneth Armstrong wrote:
> I used kvm/virt-manager heavily in Fedora 11 (helped me a GREAT deal
> in getting my RHCT).
> 
> Now, I'm trying to use it again in Fedora 13 to prepare for my RHCE,
> but I'm finding it a LOT slower.  I can't install with an ISO image on
> my external driver (using ntfs-3g), it keeps failing with a
> permissions error.  However, if I copy my ISO over to my home folder,
> and it picks it up.  

This has to do with libvirt now running VMs as the unprivileged 'qemu'
user. Probably a result of not being able to set an selinux label on the
media. You might be able to work around it by temporarily disabling
selinux with 'getenforce 0'

I also tried using the actual RHEL 5.5 and 5.4
> CD's that I have to install from, but even though it's mounted and I
> can view the contents in Nautilus, virt-manager says that /dev/sr0 has
> no media present.
> 

I believe F13 doesn't do CDROM media polling by default anymore. On F12
at least this can be changed with:

hal-disable-polling --device /dev/sr0 --enable-polling

There is also a virt-manager fix upstream to allow using a CDROM device
even if no media was detected. Fix will be backported shortly:

https://bugzilla.redhat.com/show_bug.cgi?id=583616

> So I tried to store the (preallocated raw) VM image on my external
> driver, but that fails too.  So I have to have my VM virtio disk file
> on the same hard drive that the ISO is on trying to do the install,
> which takes nearly 20 hours installing RHEL 5.4.
> 
> I did manage to get 5.5 installed before on this (by leaving it
> running overnight), but the performance was terrible.
> 

Like Rich said, maybe new VMs were accidentally using plain QEMU.
virt-manager in F13 does a poor job warning about this situation, but
rawhide is better, and the patches will be backported:

https://bugzilla.redhat.com/show_bug.cgi?id=582324

> Also, I thought Fedora 13 was supposed to automagically set up virtual
> bridges for the VMs to use, but the only option I have is NAT, it says
> that there are no bridges configured, even though I have a virbr0
> interface when I run ifconfig.
> 

virbr0 is the virtual bridge device created for NAT networking, it's not
a 'shared physical device' type bridge that gives your VMs a real IP
address. We don't create one of the latter out of the box.

- Cole