vfio-isolate is a command linux tool for Linux, which aims to facilitate CPU and memory isolation for running virtual machines with guaranteed latency.
Usage: vfio-isolate [OPTIONS] COMMAND1 [ARGS]... [COMMAND2 [ARGS]...]...
Options:
-v, --verbose enable verbose output
-d, --debug enable debug output
-u, --undo-file <undo-file> Create a file that describes the operations
needed to undo
--help Show this message and exit.
Commands:
compact-memory compact memory
cpu-governor set the CPU governor for the given CPUs
cpuset-create create a cpuset
cpuset-delete delete a cpuset
drop-caches drop caches
irq-affinity manipulate the IRQ affinity
move-tasks move tasks between cpusets
restore restore a previous state using an undo file
To "partion" your CPU between the host and your VM, a mechanism of the Linx kernel, named "cpusets" is used. Cpusets define the subset of cores are allowed to be scheduled on, but also have some other properties:
| Feature | Description |
|---|---|
| cpu-exclusivity | prevents other sibling cpusets to use the cpus of this cpuset |
| mem-exclusivity | prevents other sibling cpusets to use the memory (NUMA) of this cpuset |
| mem-migration | only effective on NUMA systems: when enabled, processes in this cpuset will have their memory migrated to the node they are running on |
| scheduler-load-balance | when enabled, the scheduler will try to load balance processes within the available cpus |
For more information, see the kernel documentation at https://www.kernel.org/doc/Documentation/cgroup-v1/cpusets.txt
In this example, we have a 6 core, 12 thread CPU from Intel, and we want to leave the first 2 cores for host, IO and emulation work, while giving the remaining 4 cores to the VM.
The command to use would be this:
# vfio-isolate \
cpuset-create --cpus C0-1,6-7 /host.slice \
cpuset-create --cpus C0-11 -nlb /machine.slice \
move-tasks / /host.slice
Notice that scheduler-load-balancing has been disabled on the machine.slice, and that there is some overlap between the two cpusets (so cpu exclusivity cannot be used), and you have to use pinning in libvirt to pin the guest cpus like this:
<vcpu placement='static'>8</vcpu>
<vcpupin vcpu="0" cpuset="2"/>
<vcpupin vcpu="1" cpuset="8"/>
<vcpupin vcpu="2" cpuset="3"/>
<vcpupin vcpu="3" cpuset="9"/>
<vcpupin vcpu="4" cpuset="4"/>
<vcpupin vcpu="5" cpuset="10"/>
<vcpupin vcpu="4" cpuset="5"/>
<vcpupin vcpu="5" cpuset="11"/>
<emulatorpin cpuset="0-1,6-7"/>
<iothreadpin iothread="1" cpuset="0-1,6-7"/>
</cputune>
To manually undo the previous command:
# vfio-isolate \
cpuset-delete /host.slice \
cpuset-delete /machine.slice
Or you could use the undo feature built into vfio-isolate (see below).
All processes in a cpuset will be moved to its parent cpuset upon deletion.
If you have a system with more than one NUMA nodes, you might want to isolate according to the different nodes. For example, on an AMD Threadripper 1920X (12 core, 24 thread), which has 2 NUMA nodes, you could do the following
# vfio-isolate \
cpuset-create --cpus N0 --mems N0 -mm /host.slice \
cpuset-create --cpus N1 --mems N1 -ce -me -mm -nlb /machine.slice \
move-tasks / /host.slice
This will configure NUMA Node 0, in this case CPU 0-5,12-17 for the host, while configuring NUMA node 1 for
the VM (6-11,18-23). The -ce/-me parameters sets the cpus/memory of NUMA node 1 to be used exclusively by this cpuset,
while the -mm parameter enables memory migration for both sets, so that processes moving into either cpuset will
have their memory migrated to the right node. Further -nlb disables scheduler load balancing.
vfio-isolate is able to record all the changes that it did and storing a recipe to undo them into a file, to be executed later.
# vfio-isolate -u /tmp/undo_description \
cpuset-create --cpus C1-4 /test.slice
This will create the test.slice cpuset, and also a file /tmp/undo_description that when executed like this
# vfio-isolate restore /tmp/undo_description
will remove test.slice. This works with all the subcommands that vfio-isolate supports.
vfio-isolate contains basic support for disabling IRQ handler execution on certain cpus:
# vfio-isolate -u /tmp/undo_irq irq-affinity mask C2-5,8-11
will prevent IRQ execution on the mentioned cpuset.
It will also write an undo description in /tmp/undo_irq which can be used to restore the previous state:
# vfio-isolate restore /tmp/undo_irq
vfio-isolate contains basic support for setting the CPU frequency governor for selected CPUs:
# vfio-isolate -u /tmp/undo_gov cpu-governor performance C2-5,8-11
will set the mentioned CPUs to performance mode.
It will also write an undo description in /tmp/undo_gov which can be used to restore the previous state:
# vfio-isolate restore /tmp/undo_gov