Re: [virtio-dev] [PATCH] virtio: introduce VIRTIO_F_RING_RESET for reset queue

[Jason Wang <jasowang@redhat.com>]

在 2021/8/23 下午4:28, Xuan Zhuo 写道:
> cc jasowang@redhat.com
>
> On Fri, 13 Aug 2021 10:31:05 +0800, 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.
> >
> > Since mmio's QueueReady allows setting 0 to stop the queue, there is no
> > need to distinguish whether VIRTIO_F_RING_RESET is negotiated.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > ---
> >   content.tex | 11 ++++++++++-
> >   1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/content.tex b/content.tex
> > index 7cec1c3..70a9765 100644
> > --- a/content.tex
> > +++ b/content.tex
> > @@ -1001,7 +1001,13 @@ \subsubsection{Common configuration structure layout}\label{sec:Virtio Transport
> >   After writing 0 to \field{device_status}, the driver MUST wait for a read of
> >   \field{device_status} to return 0 before reinitializing the device.
> >
> > -The driver MUST NOT write a 0 to \field{queue_enable}.
> > +If the VIRTIO_F_RING_RESET feature bit is not negotiated,
> > +the driver MUST NOT write a 0 to \field{queue_enable}.
> > +
> > +Otherwise, if the VIRTIO_F_RING_RESET feature bit is negotiated,
> > +the driver can stop using the queue by writing a 0 to \field{queue_enable} and
> > +MUST read the value back to ensure synchronization. Then optionally re-enable
> > +the queue.



So I think we need to clarify what did "stop" mean here. Since you're 
use "RESET" in the feature I guess the virtqueue state is also reset. 
That's fine but I'm not sure if MMIO has the similar semantic.

E.g is the virtqueue state preserved during a stop and resume?

Thanks


> >   \subsubsection{Notification structure layout}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout / Notification capability}
> >
> > @@ -6672,6 +6678,9 @@ \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.
> > +
> >   \end{description}
> >
> >   \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
> > --
> > 2.31.0
> >
> >
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