Re: [RFC PATCH v4 00/20] vDPA shadow virtqueue

[Jason Wang]

On Tue, Oct 12, 2021 at 11:59 AM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 在 2021/10/1 下午3:05, Eugenio Pérez 写道:
> > This series enable shadow virtqueue (SVQ) for vhost-vdpa devices. This
> > is intended as a new method of tracking the memory the devices touch
> > during a migration process: Instead of relay on vhost device's dirty
> > logging capability, SVQ intercepts the VQ dataplane forwarding the
> > descriptors between VM and device. This way qemu is the effective
> > writer of guests memory, like in qemu's virtio device operation.
> >
> > When SVQ is enabled qemu offers a new vring to the device to read
> > and write into, and also intercepts kicks and calls between the device
> > and the guest. Used buffers relay would cause dirty memory being
> > tracked, but at this RFC SVQ is not enabled on migration automatically.
> >
> > It is based on the ideas of DPDK SW assisted LM, in the series of
> > DPDK's https://patchwork.dpdk.org/cover/48370/ . However, these does
> > not map the shadow vq in guest's VA, but in qemu's.
> >
> > For qemu to use shadow virtqueues the guest virtio driver must not use
> > features like event_idx or indirect descriptors. These limitations will
> > be addressed in later series, but they are left out for simplicity at
> > the moment.
> >
> > SVQ needs to be enabled with QMP command:
> >
> > { "execute": "x-vhost-enable-shadow-vq",
> >        "arguments": { "name": "dev0", "enable": true } }
> >
> > This series includes some patches to delete in the final version that
> > helps with its testing. The first two of the series freely implements
> > the feature to stop the device and be able to retrieve its status. It's
> > intended to be used with vp_vpda driver in a nested environment. This
> > driver also need modifications to forward the new status bit.
> >
> > Patches 2-8 prepares the SVQ and QMP command to support guest to host
> > notifications forwarding. If the SVQ is enabled with these ones
> > applied and the device supports it, that part can be tested in
> > isolation (for example, with networking), hopping through SVQ.
> >
> > Same thing is true with patches 9-13, but with device to guest
> > notifications.
> >
> > The rest of the patches implements the actual buffer forwarding.
> >
> > Comments are welcome.
>
>
> Hi Eugenio:
>
>
> It would be helpful to have a public git repo for us to ease the review.
>
> Thanks
>

Btw, we also need to measure the performance impact of the shadow virtqueue.

Thanks