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I had a server running kvm that was upgraded from ubuntu 13.10 to 14.04 and since the upgrade after a couple of hours (in some cases less) the guest machines (a mix of linux and windows, using both virtio, realtek and intel as network interfaces), start to have network problems.

Pinging them shows that now and then the ping goes from a couple of miliseconds to several seconds. Also when connected to the guest using virt-manager when the ping goes through the roof the guest connection also freezes, although pinging the host never goes over 10ms.

I already tried several things: change network interface type (virtio, etc), pinning vcpus, adding <driver name='qemu'/> to the guests' config, disable and reenable the guest network and even upgrading the packages using this ppa:ubuntu-virt/virt-daily-upstream, but only rebooting the guest temporally solves this.

Any ideas? I am considering going back to 13.10.

1 Answer 1

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Disabling KSM appears to solve this (with the downside of having it disabled) - all the credits goes to Serge Hallyn from ubuntu team for suggesting it.

There appears to be a bug (or several) related with KSM on ubuntu 14.04, you can find a couple here and here.

To disable it, edit /etc/default/qemu-kvm and change this line:

KSM_ENABLED=1

to

KSM_ENABLED=0

then restart qemu

sudo restart qemu-kvm

I'll update this again if this is sorted out so it is possible to have KSM enabled again.

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  • This appears to be sorted out (currently testing). This bug report suggests installing the kernel image from here and re-enabling KSM.
    – mndo
    Jul 28, 2014 at 12:01
  • I had the same issue -- which was a massive show stopper for my site -- and disabling KSM stopped it from happening. Thanks! Aug 7, 2014 at 23:06

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