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When installing qemu-kvm on a VM, KSM is enabled.
I have encountered this problem in trusty:$ lsb_release -a
Distributor ID: Ubuntu
Description: Ubuntu 14.04.1 LTS
Release: 14.04
Codename: trusty
$ uname -a
Linux juju-gema-machine-2 3.13.0-40-generic #69-Ubuntu SMP Thu Nov 13 17:53:56
UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
The way to see the behaviour:
1) $ more /sys/kernel/mm/ksm/run
0
2) $ sudo apt-get install qemu-kvm
3) $ more /sys/kernel/mm/ksm/run
1
To see the soft lockups, deploy a cloud on a virtualised env like ctsstack, run
tempest on it, the compute nodes of the virtualised deployment will eventually
stop responding with (run tempest 2 times at least):
24096.072003] BUG: soft lockup - CPU#0 stuck for 23s! [qemu-system-x86:24791]
[24124.072003] BUG: soft lockup - CPU#0 stuck for 23s! [qemu-system-x86:24791]
[24152.072002] BUG: soft lockup - CPU#0 stuck for 22s! [qemu-system-x86:24791]
[24180.072003] BUG: soft lockup - CPU#0 stuck for 22s! [qemu-system-x86:24791]
[24208.072004] BUG: soft lockup - CPU#0 stuck for 22s! [qemu-system-x86:24791]
[24236.072004] BUG: soft lockup - CPU#0 stuck for 22s! [qemu-system-x86:24791]
[24264.072003] BUG: soft lockup - CPU#0 stuck for 22s! [qemu-system-x86:24791]
I am not sure whether the problem is that we are enabling KSM on a VM or
the problem is that nested KSM is not behaving properly. Either way I
can easily reproduce, please contact me if you need further details.
** Affects: qemu-kvm (Ubuntu)
Importance: Undecided
Status: New
** Tags: cts
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qemu-kvm package enables KSM on VMs
https://bugs.launchpad.net/bugs/1413540
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