mirror of
https://github.com/cloud-hypervisor/cloud-hypervisor.git
synced 2024-11-05 03:21:13 +00:00
888a465232
Explain the reason why using vDPA might be interesting and how to use it with Cloud Hypervisor. Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
155 lines
3.8 KiB
Markdown
155 lines
3.8 KiB
Markdown
# Virtio Data Path Acceleration
|
|
|
|
vDPA aims at achieving bare-metal performance for devices passed into a virtual
|
|
machine. It is an alternative to VFIO, as it provides a simpler solution for
|
|
achieving migration.
|
|
|
|
It is a kernel framework introduced recently to handle devices complying with
|
|
the VIRTIO specification on their data-path, while the control path is vendor
|
|
specific. In practice, virtqueues are accessed directly through DMA mechanism
|
|
between the hardware and the guest. The control path is accessed through the
|
|
vDPA framework, being exposed through the vhost interface as a vhost-vdpa
|
|
device.
|
|
|
|
Because DMA accesses between device and guest are going through virtqueues,
|
|
migration can be achieved without requiring device's driver to implement any
|
|
specific migration support. In case of VFIO, each vendor is expected to provide
|
|
an implementation of the VFIO migration framework, complicating things as it
|
|
must be done for each and every device's driver.
|
|
|
|
The official [website](https://vdpa-dev.gitlab.io/) contains some extensive
|
|
documentation on the topic.
|
|
|
|
## Usage
|
|
|
|
`VdpaConfig` (known as `--vdpa` from the CLI perspective) contains the list of
|
|
parameters available for the vDPA device.
|
|
|
|
```rust
|
|
struct VdpaConfig {
|
|
path: PathBuf,
|
|
num_queues: usize,
|
|
id: Option<String>,
|
|
pci_segment: u16,
|
|
}
|
|
```
|
|
|
|
```
|
|
--vdpa <vdpa> vDPA device "path=<device_path>,num_queues=<number_of_queues>,iommu=on|off,id=<device_id>,pci_segment=<segment_id>"
|
|
```
|
|
|
|
### `path`
|
|
|
|
Path of the vDPA device. Usually `/dev/vhost-vdpa-X`.
|
|
|
|
This parameter is mandatory.
|
|
|
|
Value is a string.
|
|
|
|
_Example_
|
|
|
|
```
|
|
--vdpa path=/dev/vhost-vdpa-0
|
|
```
|
|
|
|
### `num_queues`
|
|
|
|
Number of virtqueues supported by the vDPA device.
|
|
|
|
This parameter is optional.
|
|
|
|
Value is an unsigned integer set to `1` by default.
|
|
|
|
_Example_
|
|
|
|
```
|
|
--vdpa path=/dev/vhost-vdpa-0,num_queues=2
|
|
```
|
|
|
|
### `id`
|
|
|
|
Identifier of the vDPA device.
|
|
|
|
This parameter is optional. If provided, it must be unique across the entire
|
|
virtual machine.
|
|
|
|
Value is a string.
|
|
|
|
_Example_
|
|
|
|
```
|
|
--vdpa path=/dev/vhost-vdpa-0,id=vdpa0
|
|
```
|
|
|
|
### `pci_segment`
|
|
|
|
PCI segment number to which the vDPA device should be attached to.
|
|
|
|
This parameter is optional.
|
|
|
|
Value is an unsigned integer of 16 bits set to `0` by default.
|
|
|
|
_Example_
|
|
|
|
```
|
|
--vdpa path=/dev/vhost-vdpa-0,pci_segment=1
|
|
```
|
|
|
|
## Example with vDPA block simulator
|
|
|
|
The vDPA framework provides a simulator with both `virtio-block` and
|
|
`virtio-net` implementations. This is very useful for testing vDPA when we
|
|
don't have access to the specific hardware.
|
|
|
|
Given the host kernel has the appropriate modules available, let's load them
|
|
all:
|
|
|
|
```
|
|
sudo modprobe vdpa
|
|
sudo modprobe vhost_vdpa
|
|
sudo modprobe vdpa_sim
|
|
sudo modprobe vdpa_sim_blk
|
|
```
|
|
|
|
Given you have the `iproute2/vdpa` tool installed, let's now create the
|
|
`virtio-block` vDPA device:
|
|
|
|
```sh
|
|
sudo vdpa dev add name vdpa-blk1 mgmtdev vdpasim_blk
|
|
sudo chown $USER:$USER /dev/vhost-vdpa-0
|
|
sudo chmod 660 /dev/vhost-vdpa-0
|
|
```
|
|
|
|
Increase the maximum locked memory to ensure setting up IOMMU mappings will
|
|
succeed:
|
|
|
|
```sh
|
|
ulimit -l unlimited
|
|
```
|
|
|
|
Start Cloud Hypervisor:
|
|
|
|
```sh
|
|
cloud-hypervisor \
|
|
--cpus boot=1 \
|
|
--memory size=1G,hugepages=on \
|
|
--disk path=focal-server-cloudimg-amd64.raw \
|
|
--kernel vmlinux \
|
|
--cmdline "root=/dev/vda1 console=hvc0" \
|
|
--vdpa path=/dev/vhost-vdpa-0,num_queues=1
|
|
```
|
|
|
|
The `virtio-block` device backed by the vDPA simulator can be found as
|
|
`/dev/vdb` in the guest:
|
|
|
|
```
|
|
cloud@cloud:~$ lsblk
|
|
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
|
|
nullb0 252:0 0 250G 0 disk
|
|
vda 254:0 0 2.2G 0 disk
|
|
├─vda1 254:1 0 2.1G 0 part /
|
|
├─vda14 254:14 0 4M 0 part
|
|
└─vda15 254:15 0 106M 0 part /boot/efi
|
|
vdb 254:16 0 128M 0 disk
|
|
```
|