Re: [virtio-dev] Re: [RFC PATCH 3/5] virtio: The actions by the device upon SUSPEND

[Jason Wang <jasowang@redhat.com>]

On Tue, Aug 15, 2023 at 7:17âPM Zhu, Lingshan <lingshan.zhu@intel.com> wrote:
>
>
>
> On 8/15/2023 8:29 AM, Jason Wang wrote:
> > On Mon, Aug 14, 2023 at 7:29âPM Zhu Lingshan <lingshan.zhu@intel.com> wrote:
> >> This commit specifies the actions to be taken by the device upon
> >> SUSPEND.
> >>
> >> Signed-off-by: Jason Wang <jasowang@redhat.com>
> >> Signed-off-by: Eugenio PÃrez <eperezma@redhat.com>
> >> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> >> ---
> >>   content.tex | 9 +++++++++
> >>   1 file changed, 9 insertions(+)
> >>
> >> diff --git a/content.tex b/content.tex
> >> index 074f43e..43bd5de 100644
> >> --- a/content.tex
> >> +++ b/content.tex
> >> @@ -96,6 +96,15 @@ \section{\field{Device Status} Field}\label{sec:Basic Facilities of a Virtio Dev
> >>   If VIRTIO_F_SUSPEND is negotiated and SUSPEND is set, the device MUST clear SUSPEND
> >>   and resumes operation upon DRIVER_OK.
> >>
> >> +If VIRTIO_F_SUSPEND is negotiated, when SUSPEND is set, the device MUST perform the following operations:
> >> +\begin{itemize}
> >> +\item Stop comsuming any descriptors
> > Typo.
> yes will fix
> >
> >> +\item Mark all finished descriptors as used and send used buffer notification to the driver
> > What happens to the unfinished descriptors?
> still in the descriptors table or considered as in-flight, we will post
> a patch tracking in-flight descriptors.

So I think we should either

1) add in-flight descriptors in this series

or

2) force a flush

To make sure the new proposed function is complete.

> >
> >> +\item Record Virtqueue State of each enabled virtqueue, see section \ref{sec:Virtqueues / Virtqueue State}
> > This basically means those states are only available after suspending
> > or not? It would be still useful for debugging if we allow it without
> > suspending.
> Yes, for now only allow to read/write the virtqueue state after setting
> SUSPEND, this is to avoid race conditions with the device.

For debugging, we don't need to care about those races. A lot of
hardware allow to expose those via e.g ethtool.

>
> Still can suspend then collect the idx for debugging?

I mean for runtime debugging.

> >
> >> +\item Pause its operation and preserve all configurations in its Device Configuration Space, see \ref{sec:Basic Facilities of a Virtio Device / Device Configuration Space}
> > We probably need to define the "pause" here (e.g what happens to the
> > inflight descriptors).
> Shall we say: freeze both its data-plane and control-plane?

I mean if we've defined "suspend" we can simply use "suspend" instead
of "pause"?

Thanks

> >
> > Thanks
> >
> >> +\item Present SUSPEND in \field{device status}
> >> +\end{itemize}
> >> +
> >>   \section{Feature Bits}\label{sec:Basic Facilities of a Virtio Device / Feature Bits}
> >>
> >>   Each virtio device offers all the features it understands.  During
> >> --
> >> 2.35.3
> >>
> >
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>