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Libvirt allows the user to define an incomplete NUMA topology, where
the sum of all CPUs in each cell is less than the total of VCPUs.
What ends up happening is that QEMU allocates the non-enumerated CPUs
in the first NUMA node. This behavior is being flagged as 'to be
deprecated' at least since QEMU commit ec78f8114bc4 ("numa: use
possible_cpus for not mapped CPUs check").
In [1], Maxiwell suggested that we forbid the user to define such
topologies. In his review [2], Peter Krempa pointed out that we can't
break existing guests, and suggested that Libvirt should emulate the
QEMU behavior of putting the remaining vCPUs in the first NUMA node
in these cases.
This patch implements Peter Krempa's suggestion. Since we're going
to most likely end up with disjointed NUMA configuration in node 0
after the auto-fill, we're making auto-fill dependent on QEMU_CAPS_NUMA.
A following patch will update the documentation not just to inform
about the auto-fill mechanic with incomplete NUMA topologies, but also
to discourage the user to create such topologies in the future. This
approach also makes Libvirt independent of whether QEMU changes
its current behavior since we're either auto-filling the CPUs in
node 0 or the user (hopefully) is aware that incomplete topologies,
although supported in Libvirt, are to be avoided.
[1] https://www.redhat.com/archives/libvir-list/2019-June/msg00224.html
[2] https://www.redhat.com/archives/libvir-list/2019-June/msg00263.html
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
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==============================
Libvirt API for virtualization
==============================
Libvirt provides a portable, long term stable C API for managing the
virtualization technologies provided by many operating systems. It
includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware
vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER
Hypervisor.
For some of these hypervisors, it provides a stateful management
daemon which runs on the virtualization host allowing access to the
API both by non-privileged local users and remote users.
Layered packages provide bindings of the libvirt C API into other
languages including Python, Perl, PHP, Go, Java, OCaml, as well as
mappings into object systems such as GObject, CIM and SNMP.
Further information about the libvirt project can be found on the
website:
https://libvirt.org
License
=======
The libvirt C API is distributed under the terms of GNU Lesser General
Public License, version 2.1 (or later). Some parts of the code that are
not part of the C library may have the more restrictive GNU General
Public License, version 2.0 (or later). See the files ``COPYING.LESSER``
and ``COPYING`` for full license terms & conditions.
Installation
============
Instructions on building and installing libvirt can be found on the website:
https://libvirt.org/compiling.html
Contributing
============
The libvirt project welcomes contributions in many ways. For most components
the best way to contribute is to send patches to the primary development
mailing list. Further guidance on this can be found on the website:
https://libvirt.org/contribute.html
Contact
=======
The libvirt project has two primary mailing lists:
* libvirt-users@redhat.com (**for user discussions**)
* libvir-list@redhat.com (**for development only**)
Further details on contacting the project are available on the website:
https://libvirt.org/contact.html