Re: [virtio-dev] Re: [PATCH v4 1/3] virtio: introduce virtqueue reset as basic facility

[Jason Wang <jasowang@redhat.com>]

On Wed, Sep 29, 2021 at 10:01 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> On Tue, 28 Sep 2021 12:06:01 +0200, Cornelia Huck <cohuck@redhat.com> wrote:
> > On Tue, Sep 28 2021, Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> >
> > > This patch allows the driver to reset a queue individually.
> > >
> > > This is very common on general network equipment. By disabling a queue,
> > > you can quickly reclaim the buffer currently on the queue. If necessary,
> > > we can reinitialize the queue separately.
> > >
> > > For example, when virtio-net implements support for AF_XDP, we need to
> > > disable a queue to release all the original buffers when AF_XDP setup.
> > > And quickly release all the AF_XDP buffers that have been placed in the
> > > queue when AF_XDP exits.
> > >
> > > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > > ---
> > >  content.tex | 45 +++++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 45 insertions(+)
> > >
> > > diff --git a/content.tex b/content.tex
> > > index 37c45d3..05b05ba 100644
> > > --- a/content.tex
> > > +++ b/content.tex
> > > @@ -407,6 +407,47 @@ \section{Exporting Objects}\label{sec:Basic Facilities of a Virtio Device / Expo
> > >  types. It is RECOMMENDED that devices generate version 4
> > >  UUIDs as specified by \hyperref[intro:rfc4122]{[RFC4122]}.
> > >

Btw, we need to add this into the section of "Virtqueues"

> > > +\section{Virtqueue Reset}\label{sec:Virtqueues / Virtqueue Reset}
> > > +
> > > +When VIRTIO_F_RING_RESET is negotiated, the driver can reset a virtqueue
> > > +individually. The way to reset the virtqueue is transport specific.
> > > +
> > > +Virtqueue reset is divided into two parts. The driver reset a queue
> > > +first, and then re-enable the queue. The re-enable part is optional.
> >
> > Maybe
> >
> > "The driver first resets a queue and can afterwards optionally re-enable
> > it."
> >
> > ?
> >
> > > +
> > > +\subsection{Virtqueue Reset}\label{sec:Virtqueues / Virtqueue Reset / Virtqueue Reset}
> > > +
> > > +\devicenormative{\subsubsection}{Virtqueue Reset}{Virtqueues / Virtqueue Reset / Virtqueue Reset}
> > > +
> > > +After a queue has been reset by the driver, the device MUST NOT execute
> > > +any requests from that virtqueue, or notify the driver for it.
> > > +
> > > +The device MUST re-initialize any state of a virtqueue that has been
> > > +reset, including available and used state.

Maybe "The device must reset any state..."

> > > +
> > > +\drivernormative{\subsubsection}{Virtqueue Reset}{Virtqueues / Virtqueue Reset / Virtqueue Reset}
> > > +
> > > +After the driver tell the device to reset a queue, the driver MUST verify that
> >
> > s/tell/tells/ (may have been my typo...)
> >
> > > +the queue has actually been reset.
> > > +
> > > +After the queue has been successfully reset, the driver MAY release any
> > > +resource associated with that virtqueue.
> > > +
> > > +\subsection{Virtqueue Re-enable}\label{sec:Virtqueues / Virtqueue Reset / Virtqueue Re-enable}
> > > +
> > > +This process is the same as the initialization process of a single queue during
> > > +the initialization of the entire device.
> > > +
> > > +\devicenormative{\subsubsection}{Virtqueue Re-enable}{Virtqueues / Virtqueue Reset / Virtqueue Re-enable}
> > > +
> > > +The device MUST receive the new configuration from the driver. (i.e. the maximum
> > > +Queue Size.)
> >
> > Maybe
> >
> > "The device MUST observe any queue configuration that may have been
> > changed by the driver, like the maximum queue size."
> >
> > Although I'm not sure about 'observe'. Anybody have a better term?

I wonder if this is implied in the queue_enable or we need to explain
the semantics of "queue_enable" instead of here. Considering we list
queue reset and basic facility, we need to explicitly add queue enable
into the basic facility first.

> >
> > > +
> > > +\drivernormative{\subsubsection}{Virtqueue Re-enable}{Virtqueues / Virtqueue Reset / Virtqueue Re-enable}
> > > +
> > > +The driver MUST apply for resources, set new configuration to the device, and
> > > +finally activate the device.
> >
> > Maybe
> >
> > "When re-enabling a queue, the driver MUST configure the queue resources
> > as during initial virtqueue discovery, but optionally with different
> > parameters."
> >
> > ?

If we make the queue enablement as a subsection, we can move this
there. Then we don't need to differ enable and re-enable.

Thanks

> >
> > What actually needs to be done is dependent on the transport anyway.
> >
> > What do you mean by "activate the device"? I thought the device state
> > remained unchanged, it is just the individual queue that is reset and
> > re-enabled?
>
> Yes.
>
> Thanks very much.
>
> >
> > > +
> > >  \chapter{General Initialization And Device Operation}\label{sec:General Initialization And Device Operation}
> > >
> > >  We start with an overview of device initialization, then expand on the
> > > @@ -6673,6 +6714,10 @@ \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits}
> > >    transport specific.
> > >    For more details about driver notifications over PCI see \ref{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI-specific Initialization And Device Operation / Available Buffer Notifications}.
> > >
> > > +  \item[VIRTIO_F_RING_RESET(40)] This feature indicates
> > > +  that the driver can reset a queue individually.
> > > +  See \ref{sec:Virtqueues / Virtqueue Reset}.
> > > +
> > >  \end{description}
> > >
> > >  \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
> >
>
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