Just a side comment, slightly OT:
On 07/14/2016 02:11 AM, Thomas Goirand wrote:
> Then every day, a periodic job in the Jessie amd64 Jenkins starts a
> check job. It installs most of OpenStack on a single machine: a read
> bare metal machine running a Jessie Live which is PXE booted, not a just
> a VM, because using Qemu to do nested virtualization is too slow to
> enable quick debugging.
Are you talking about plain QEMU or nested KVM? Sure, in the default
configuration, starting QEMU within a QEMU/KVM instance will not be
virtualized and just use emulation (and hence be terribly slow), but
at least on x86_64 (both Intel and AMD) there is support for using
nested KVM, by enabling the nested option.
Just create /etc/modprobe.d/nested-kvm.conf with the following
contents on the _host_:
options kvm-intel nested=1
options kvm-amd nested=1
And either reboot the host or reload the KVM modules (all VMs need
to be stopped for that). Then KVM support is available within VMs
started on that host, provided that CPU QEMU emulates has the KVM
feature. You can enable that either via the following QEMU CPU
options:
1. -cpu host (copies host CPU configuration)
2. -cpu kvm64,+vmx,+lahf_lm (Intel processors)
-cpu kvm64,+svm,+lahf_lm (AMD processors)
(You best detect which via looking at /proc/cpuinfo of the host
and seeing if either vmx or svm is in the flags there.)
From my experience, while that is a bit slower than doing that on
bare metal, the performance is actually quite reasonable, at least
if you use virtio for I/O (both in the outer and inner VMs). The
main issue is actually that you need to allocate enough RAM for the
outer VM.
Regards,
Christian
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