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The nodeinfo is reporting incorrect number of cpus and incorrect host topology on PPC64 KVM hosts. The KVM hypervisor on PPC64 needs only the primary thread in a core to be online, and the secondaries offlined. While scheduling a guest in, the kvm scheduler wakes up the secondaries to run in guest context. The host scheduling of the guests happen at the core level(as only primary thread is online). The kvm scheduler exploits as many threads of the core as needed by guest. Further, starting POWER8, the processor allows splitting a physical core into multiple subcores with 2 or 4 threads each. Again, only the primary thread in a subcore is online in the host. The KVM-PPC scheduler allows guests to exploit all the offline threads in the subcore, by bringing them online when needed. (Kernel patches on split-core http://www.spinics.net/lists/kvm-ppc/msg09121.html) Recently with dynamic micro-threading changes in ppc-kvm, makes sure to utilize all the offline cpus across guests, and across guests with different cpu topologies. (https://www.mail-archive.com/kvm@vger.kernel.org/msg115978.html) Since the offline cpus are brought online in the guest context, it is safe to count them as online. Nodeinfo today discounts these offline cpus from cpu count/topology calclulation, and the nodeinfo output is not of any help and the host appears overcommited when it is actually not. The patch carefully counts those offline threads whose primary threads are online. The host topology displayed by the nodeinfo is also fixed when the host is in valid kvm state. Signed-off-by: Shivaprasad G Bhat <sbhat@linux.vnet.ibm.com> Signed-off-by: Andrea Bolognani <abologna@redhat.com>
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>