kernel-packages team mailing list archive

[Chris J Arges <1344430@xxxxxxxxxxxxxxxxxx>]

One thing we are looking at is potential issues with KSM and KVM. Can you try disabling KSM and see if the results remain the same:
- edit /etc/default/qemu:
- change KSM_ENABLED to 0
- sudo service qemu restart 
I would recommend doing this when your VMs are shutdown; and ensuring nothing else in your system is using KSM.

Thanks,

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https://bugs.launchpad.net/bugs/1344430

Title:
  10-15% iowait on kvm instances on Ubuntu 14.04

Status in “linux” package in Ubuntu:
  Confirmed

Bug description:
  After upgrading from Ubuntu 12.04 to Ubuntu 14.04 we began seeing
  10-15% iowait on kvm guests.  The guests had little to no load and yet
  the shell was laggy and commands took forever to respond (assuming you
  could even type them)

  # 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 posted to Ubuntu Server and they suggested that I upgrade my kernel
  version.

  Relevant Mailing List discussion:

  https://lists.ubuntu.com/archives/ubuntu-server/2014-July/006925.html

  After installing a 3.14 kernel the performance returned to normal.

  kvm-andromeda:~# uname -a
  Linux kvm-andromeda 3.14.1-031401-generic #201404141220 SMP Mon Apr 14 16:21:48 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
  --- 
  ApportVersion: 2.14.1-0ubuntu3.2
  Architecture: amd64
  DistroRelease: Ubuntu 14.04
  Package: linux (not installed)
  ProcEnviron:
   TERM=screen
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  Tags:  trusty
  Uname: Linux 3.14.1-031401-generic x86_64
  UnreportableReason: The running kernel is not an Ubuntu kernel
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: root
  _MarkForUpload: True

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