10-15% iowait on kvm instances on Ubuntu 14.04

[Serge Hallyn]

Quoting William Van Hevelingen (wvan13 at gmail.com):
> Hi All,
> 
> Does anyone know about any known issues with KVM on Ubuntu Trusty?
> 
> We're seeing 10-15% iowait on some instances that are essentially idling.
> Two different hypervisors are showing the same symptoms. We had no issues
> when we were running them on Precise with less powerful machines.
> 
> We're using the paravirtual drivers for the instances disk_type.
> 
> 
> # uname -a
> Linux kvm-andromeda 3.13.0-29-generic #53-Ubuntu SMP Wed Jun 4 21:00:20 UTC
> 2014 x86_64 x86_64 x86_64 GNU/Linux
> 
> # kvm --version
> QEMU emulator version 2.0.0 (Debian 2.0.0+dfsg-2ubuntu1.1), Copyright (c)
> 2003-2008 Fabrice Bellard

I haven't, but in order to see whether the problem is qemu or the kernel,
I would try (a) using the canonical-kernel-team upstream kernel build, with
stock trusty qemu, and then (b) use the stock trusty kernel with the
qemu built at ppa:ubuntu-virt/virt-daily-upstream

-serge