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Subject: Re: [PATCH v3 1/2] virtio: introduce virtqueue reset as basic facility


On Tue, 28 Sep 2021 11:01:55 +0800, Jason Wang <jasowang@redhat.com> wrote:
> On Mon, Sep 27, 2021 at 8:32 PM 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 | 41 +++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 41 insertions(+)
> >
> > diff --git a/content.tex b/content.tex
> > index 37c45d3..603b1f1 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -407,6 +407,43 @@ \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]}.
> >
> > +\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 MUST reset stop a queue
> > +first, and then re-enable the queue. The re-enable part is optional.
> > +
> > +\devicenormative{\subsection}{Virtqueue Reset Stop}{Virtqueues / Virtqueue Reset}
> > +The device MUST not executes the requests from this virtqueue, and notify the
> > +driver.
> > +
> > +And the device MUST initialize all states of this virtqueue, including the
> > +available state and the used state.
> > +
> > +\drivernormative{\subsection}{Virtqueue Reset Stop}{Virtqueues / Virtqueue Reset}
> > +
> > +The driver MUST first notify
>
> What did "notify" mean here? I guess it means the transport specific
> way to stop a virtqueue?

Yes.

Cornelia Huck suggested that this expression would be better:

	After the driver tell the device to reset a queue, the driver MUST verify that
	the queue has actually been reset.

Thanks.


>
> Thanks
>
> > the device and confirm that we have successfully
> > +stopped a queue.
> > +
> > +Then the driver can release all the resources occupied by this virtqueue.
> > +And reinitialize the state of this queue.
> > +
> > +\devicenormative{\subsection}{Virtqueue Reset Re-enable}{Virtqueues / Virtqueue Reset}
> > +
> > +This process is the same as the initialization process of a single queue during
> > +the initialization of the entire device. After the device has accepted all the
> > +configuration from the driver, it will start working under the notification of the
> > +driver.
> > +
> > +\drivernormative{\subsection}{Virtqueue Reset Re-enable}{Virtqueues / Virtqueue Reset}
> > +
> > +This process is the same as the initialization process of a single queue during
> > +the entire device initialization process. After the driver allocates resources
> > +and completes the configuration of the queue status, it notifies the device to
> > +start working.
> > +
> >  \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 +6710,10 @@ \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}
> > --
> > 2.31.0
> >
>


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