Re: [virtio] [PATCH v6 4/5] packed virtqueues: more efficient virtqueue layout

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 10 Jan 2018 11:47:58 +0200
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> Performance analysis of this is in my kvm forum 2016 presentation.  The
> idea is to have a r/w descriptor in a ring structure, replacing the used
> and available ring, index and descriptor buffer.

Do we have a place to store pointers to such information?

> 
> This is also easier for devices to implement than the 1.0 layout.
> Several more enhancements will be necessary to actually make this
> efficient for devices to use.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>  content.tex     |  36 ++-
>  packed-ring.tex | 668 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 701 insertions(+), 3 deletions(-)
>  create mode 100644 packed-ring.tex
> 
> diff --git a/content.tex b/content.tex
> index 3b4579e..3059bd3 100644
> --- a/content.tex
> +++ b/content.tex

(...)

> @@ -5199,10 +5215,19 @@ Currently these device-independent feature bits defined:
>  \begin{description}
>    \item[VIRTIO_F_RING_INDIRECT_DESC (28)] Negotiating this feature indicates
>    that the driver can use descriptors with the VIRTQ_DESC_F_INDIRECT
> -  flag set, as described in \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / The Virtqueue Descriptor Table / Indirect Descriptors}~\nameref{sec:Basic Facilities of a Virtio Device / Virtqueues / The Virtqueue Descriptor Table / Indirect Descriptors}.
> +  flag set, as described in \ref{sec:Basic Facilities of a Virtio
> +Device / Virtqueues / The Virtqueue Descriptor Table / Indirect
> +Descriptors}~\nameref{sec:Basic Facilities of a Virtio Device /
> +Virtqueues / The Virtqueue Descriptor Table / Indirect
> +Descriptors} and
> +  \ref{sec:Packed Virtqueues / Indirect Flag: Scatter-Gather Support}
> +\ref{sec:Packed Virtqueues / Driver and Device Event Suppression}.

That one needs to go below (copy/paste error?).

>  
>    \item[VIRTIO_F_RING_EVENT_IDX(29)] This feature enables the \field{used_event}
> -  and the \field{avail_event} fields as described in \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / Virtqueue Interrupt Suppression} and \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / The Virtqueue Used Ring}.
> +  and the \field{avail_event} fields as described in
> +\ref{sec:Basic Facilities of a Virtio Device / Virtqueues /
> +Virtqueue Interrupt Suppression}, \ref{sec:Basic Facilities of a Virtio Device / Virtqueues / The Virtqueue Used Ring}
> +and .

Here's where the ref above needs to go.

>  
>    \item[VIRTIO_F_VERSION_1(32)] This indicates compliance with this
>      specification, giving a simple way to detect legacy devices or drivers.
> @@ -5212,6 +5237,9 @@ Currently these device-independent feature bits defined:
>    addresses in memory.  If this feature bit is set to 0, then the device emits
>    physical addresses which are not translated further, even though an IOMMU
>    may be present.
> +  \item[VIRTIO_F_RING_PACKED(34)] This feature indicates
> +  support for the packed virtqueue layout as described in
> +\ref{sec:Basic Facilities of a Virtio Device / Packed Virtqueues}.
>  \end{description}

I think the references should include a title as well (that makes the
resulting document easier to read).

>  
>  \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}