formatdomain.html.in: document emulator/vcpu pin delay

In a guest with only one vcpu, when pinning the emulator in say CPU184 and the vcpu0 in CPU0 of the host, the user might expect that only CPU0 and CPU184 of the host will be used by the guest.

The reality is that Libvirt takes some time to honor the emulator and vcpu pinning, taking care of NUMA constraints first. This will result in other CPUs of the host being potentially used by the QEMU thread until the emulator/vcpu pinning is done. The user then might be confused by the output of ‘virsh cpu-stats’ in this scenario, showing around 200 microseconds of cycles being spent in other CPUs.

Let’s document this behavior, which is explained in detail in Libvirt commit v5.0.0-199-gf136b83139, in the cputune section of formatdomain.html.in.

Signed-off-by: Daniel Henrique Barboza danielhb413@gmail.com Reviewed-by: Andrea Bolognani abologna@redhat.com

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

Libvirt uses the GNU Autotools build system, so in general can be built and installed with the usual commands, however, we mandate to have the build directory different than the source directory. For example, to build in a manner that is suitable for installing as root, use:

$ mkdir build && cd build
$ ../configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var
$ make
$ sudo make install

While to build & install as an unprivileged user

$ mkdir build && cd build
$ ../configure --prefix=$HOME/usr
$ make
$ make install

The libvirt code relies on a large number of 3rd party libraries. These will be detected during execution of the configure script and a summary printed which lists any missing (optional) dependencies.

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