mirror of
https://github.com/cloud-hypervisor/cloud-hypervisor.git
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57 lines
2.3 KiB
Markdown
57 lines
2.3 KiB
Markdown
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# Cloud Hypervisor Hot Plug
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Currently Cloud Hypervisor only support hot plugging of CPU devices.
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## Kernel support
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For hotplug on Cloud Hypervisor ACPI GED support is needed. This can either be achieved by turning on `CONFIG_ACPI_REDUCED_HARDWARE_ONLY`
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or by using this kernel patch (available in 5.5rc1 and later): https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/drivers/acpi/Makefile?id=ac36d37e943635fc072e9d4f47e40a48fbcdb3f0
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This patch is integrated into the Clear Linux KVM and cloudguest images.
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## CPU Hot Plug
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Extra vCPUs can be added (but not removed [1]) from a running Cloud Hypervisor instance. This is controlled by two mechanisms:
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1. Specifying a number of maximum potential vCPUs that is greater than the number of default (boot) vCPUs.
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2. Making a HTTP API request to the VM to ask for the additional vCPUs to be added.
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To use CPU hotplug start the VM with the number of max vCPUs greater than the number of boot vCPUs, e.g.
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```shell
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$ pushd $CLOUDH
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$ sudo setcap cap_net_admin+ep ./cloud-hypervisor/target/release/cloud-hypervisor
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$ ./cloud-hypervisor/target/release/cloud-hypervisor \
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--kernel ./hypervisor-fw \
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--disk path=clear-31890-kvm.img \
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--cpus boot=4,max=8 \
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--memory size=1024M \
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--net "tap=,mac=,ip=,mask=" \
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--rng \
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--api-socket=/tmp/ch-socket
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$ popd
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```
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Notice the addition of `--api-socket=/tmp/ch-socket` and a `max` parameter on `--cpus boot=4.max=8`.
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To ask the VMM to add additional vCPUs then use the resize API:
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```shell
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curl -H "Accept: application/json" -H "Content-Type: application/json" -i -XPUT --unix-socket /tmp/ch-socket -d "{ \"desired_vcpus\":8}" http://localhost/api/v1/vm.resize
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```
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The extra vCPU threads will be created and advertised to the running kernel. The kernel does not bring up the CPUs immediately and instead the user must "on-line" them from inside the VM:
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```shell
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root@ch-guest ~ # lscpu | grep list:
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On-line CPU(s) list: 0-3
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Off-line CPU(s) list: 4-7
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root@ch-guest ~ # echo 1 | tee /sys/devices/system/cpu/cpu[4,5,6,7]/online
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1
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root@ch-guest ~ # lscpu | grep list:
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On-line CPU(s) list: 0-7
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```
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After a reboot the added CPUs will remain.
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[1]: It is not currently possible to remove CPUs after they are added however CPU hot unplug is included in our roadmap for a future version.
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