0cc6f8931f
Links between NUMA nodes can have different latencies and
bandwidths. This info is newly defined in ACPI 6.2 under
Heterogeneous Memory Attribute Table (HMAT) table. Linux kernel
learned how to report these values under sysfs and thus we can
expose them in our capabilities XML. The sysfs interface is
documented in kernel's Documentation/admin-guide/mm/numaperf.rst.
Long story short, two nodes can be in initiator-target
relationship. A node can be initiator if it has a CPU or a device
that's capable of initiating memory transfer. Therefore a node
that has just memory can only be target. An initiator-target link
can then have any combination of {bandwidth, latency} - {access,
read, write} attribute (6 in total). However, the standard says
access is applicable iff read and write values are the same.
Therefore, we really have just four combinations of attributes:
bandwidth-read, bandwidth-write, latency-read, latency-write.
This is the combination that kernel reports anyway.
Then, under /sys/system/devices/node/nodeX/acccessN/initiators we
find values for those 4 attributes and also symlinks named
"nodeN" which then represent initiators to nodeX. For instance:
/sys/system/node/node1/access1/initiators/node0 -> ../../node0
/sys/system/node/node1/access1/initiators/read_bandwidth
/sys/system/node/node1/access1/initiators/read_latency
/sys/system/node/node1/access1/initiators/write_bandwidth
/sys/system/node/node1/access1/initiators/write_latency
This means that node0 is initiator and node1 is target and values
of the interconnect can be read.
In theory, there can be separate links to memory side caches too
(e.g. one link from node X to node Y's main memory, another from
node X to node Y's L1 cache, another one to L2 cache and so on).
But sysfs does not express this relationship just yet.
The "accessN" means either "access0" or "access1". The difference
is that while the former expresses the best interconnect between
two nodes including CPUS and I/O devices (such as GPUs and NICs),
the latter includes only CPUs and thus is what we need.
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1786309
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@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:
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: