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Message #99868
[Bug 1368439] Re: Random high latency with KSM enabled and multiple CPU sockets
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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