Re: [virtio-comment] [PATCH 0/5] virtio: introduce SUSPEND bit and vq state

["Zhu, Lingshan" <lingshan.zhu@intel.com>]

On 9/6/2023 9:49 PM, Michael S. Tsirkin wrote:
> On Wed, Sep 06, 2023 at 04:38:44PM +0800, Zhu, Lingshan wrote:
> > On 9/6/2023 4:29 PM, Michael S. Tsirkin wrote:
> > > On Wed, Sep 06, 2023 at 04:16:32PM +0800, Zhu Lingshan wrote:
> > > > This series introduces
> > > > 1)a new SUSPEND bit in the device status
> > > > Which is used to suspend the device, so that the device states
> > > > and virtqueue states are stabilized.
> > > >
> > > > 2)virtqueue state and its accessor, to get and set last_avail_idx
> > > > and last_used_idx of virtqueues.
> > > >
> > > > The main usecase of these new facilities is Live Migration.
> > > >
> > > > Future work: dirty page tracking and in-flight descriptors.
> > > oh that answers my question - it's not covered.
> > > I don't think we can merge this without in-flight descriptor
> > > support.
> > When SUSPEND, we require the device wait until all descriptors that
> > being processed to finish and mark them as used.(In patch 2)
> > at this point there may be no in-flight descriptors, so this is still
> > self-consistent. The tracker for in-flight descriptors is excluded to
> > make this series small and focus.
> Does not work generally.
> Imagine RX ring of a network device for example. You can wait
> as long as you can but if there's no incoming network traffic
> buffers will not be used.
Yes we will include a patch tracking in-flight descriptors in V2.
> Also please, keep to the spec terminology. buffers are used not
> descriptors. Best to keep it straight errors will not leak into
> spec.
OK
> > > > This series addresses many comments from Jason, Stefan and Eugenio
> > > > from RFC series.
> > > >
> > > > Zhu Lingshan (5):
> > > >     virtio: introduce vq state as basic facility
> > > >     virtio: introduce SUSPEND bit in device status
> > > >     virtqueue: constraints for virtqueue state
> > > >     virtqueue: ignore resetting vqs when SUSPEND
> > > >     virtio-pci: implement VIRTIO_F_QUEUE_STATE
> > > >
> > > >    content.tex       | 118 ++++++++++++++++++++++++++++++++++++++++++++++
> > > >    transport-pci.tex |  18 +++++++
> > > >    2 files changed, 136 insertions(+)
> > > >
> > > > --
> > > > 2.35.3
> > > >
> > > >
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> > > > OASIS Virtual I/O Device (VIRTIO) TC.
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