kernel-packages team mailing list archive

[Serge Hallyn <1368439@xxxxxxxxxxxxxxxxxx>]

Is this still an issue for you?

There were some actual KSM corruption bugs which were somewhat recently
fixed.

KSM in general wil use more CPU in order to reduce memory contention, so
your results are not necessarily unexpected.  Aside from turning KSM
off, you can also reduce the KSM frequency.

There are some other tuning hints at http://www.linux-
kvm.org/page/Tuning_Kernel

** Changed in: qemu-kvm (Ubuntu)
       Status: New => Incomplete

** Changed in: qemu-kvm (Ubuntu)
   Importance: Undecided => Low

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https://bugs.launchpad.net/bugs/1368439

Title:
  Random high latency with KSM enabled and multiple CPU sockets

Status in linux package in Ubuntu:
  Incomplete
Status in qemu-kvm package in Ubuntu:
  Incomplete

Bug description:
  If running a box with multiple CPU sockets and Ubuntu 14.04 Server
  64-bit qemu-kvm with KSM enabled as by default, random high latency
  occurs on network connections for VMs, as high as 4000ms - 5000ms. The
  host also reports high IO wait times.

  Disabling KSM fixed this for me.

  I run the same setup on boxes with only 1 CPU socket and it's not an
  issue.

  qemu-kvm version: Installed: 2.0.0+dfsg-2ubuntu1.3

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