kvm guest network issue


Order

I have a server running kvm that has been upgraded from ubuntu 13.10 to 14.04 and since the upgrade takes hours (less in some cases) client machines (mix of linux and windows, using both virtio, realtek and intel as the network interface)), network problems started to occur.

Pinging them shows that the ping sometimes goes from milliseconds to seconds. Likewise, when using virt-manager to connect to the guest while pinging through the roof, the guest connection will freeze, although the ping to the host will never take more than 10ms.

I've tried several things: changing the network interface type (virtio, etc.), pinning the vcpus, adding <driver name='qemu'/>to the guest's config, disabling and re-enabling the guest network, and even using this to upgrade packages ppa:ubuntu-virt/virt-daily-upstream, but only rebooting the guest solves this temporarily question.

Any ideas? I'm thinking of going back to 13.10.

Order

Disabling KSM seems to fix this (with the downside of disabling it) - all credit to the ubuntu team goes to Serge Hallyn for suggesting this.

There seems to be one (or several) KSM related bugs on ubuntu 14.04, you can find a pair here and here .

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

KSM_ENABLED=1

arrive

KSM_ENABLED=0

Then restart qemu

sudo restart qemu-kvm

If this is fixed, I will update it again so that it is possible to enable KSM again.

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