kernel-packages team mailing list archive

[Serge Hallyn <1341195@xxxxxxxxxxxxxxxxxx>]

Quoting Tamas Papp (1341195@xxxxxxxxxxxxxxxxxx):
> On 07/16/2014 06:35 PM, Serge Hallyn wrote:
> 
> 
> > To be clear, you have not yet gotten the bug since you've set
> > KSM_ENABLED to 0, or have you?
> 
> I just did it, so no, not yet.
> 
> This happened by time:
> 
> Saucy (everything is fine) -> Trusty (issue happened) -> Trusty with 
> Saucy kernel 3 weeks ago (no issue) -> today with 3 weeks uptime (issue 
> happened) -> KSM_ENABLED=0 + reboot with Trusty kernel -> now
> 
> I just want to be clear, that both of us understand the same on this.
> 
> 
> > Interesting about the saucy kernel.  Ideally we could reproduce this
> > reliably enough to really bisect.
> >
> > I wonder if we can reproduce without qemu.
> 
> 
> I have a some other servers with LXC with no issue, If there is KVM, 
> then issue happens.
> Does it really not show up anywhere else?

I've personally not seen it, and noone on my team, who use a lot of
kvm instances, has seen it.  Our two current theories are that (a) it
has to do with ksm page migration across numa-nodes, or (b) it has to
do with a race with transparent hugepages versus ksm.  For (b) there is
already a commit in Linus' tree (f72e7dcd).  For (a), you can probably
test by setting /sys/kernel/mm/ksm/merge_across_nodes to 0.  (We are
trying these as well, but as the testcases are not 100% positive
it'd be good to have you try as well)

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https://bugs.launchpad.net/bugs/1341195

Title:
  KVM guests getting slow by time

Status in “linux” package in Ubuntu:
  Incomplete
Status in “qemu” package in Ubuntu:
  Incomplete

Bug description:
  There is a post with very similar symptoms on serverfault:

  http://serverfault.com/questions/609881/windows-server-2012-on-kvm-on-
  ubuntu-14-04-runs-well-for-a-while-and-then-slows/612084#612084

  
  Basically all kind of KVM guests are getting slow by time, both windows or linux. The more running guests, it happens sooner.
  Switching back to Saucy kernel is a good workaround.

  ProblemType: Bug
  DistroRelease: Ubuntu 14.04
  Package: qemu-kvm 2.0.0+dfsg-2ubuntu1.1
  ProcVersionSignature: Ubuntu 3.13.0-29.53-generic 3.13.11.2
  Uname: Linux 3.13.0-29-generic x86_64
  NonfreeKernelModules: zfs zunicode zavl zcommon znvpair
  ApportVersion: 2.14.1-0ubuntu3.2
  Architecture: amd64
  Date: Sat Jul 12 22:18:49 2014
  SourcePackage: qemu
  UpgradeStatus: No upgrade log present (probably fresh install)

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