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

[Michael S. Tsirkin]

On Wed, Jan 10, 2018 at 03:15:38PM +0100, Cornelia Huck wrote:
> On Wed, 10 Jan 2018 11:47:58 +0200
> "Michael S. Tsirkin"  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 
> > ---
> >  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).

Want to add a macro including ref+nameref?
We'd use it for all sec: references then.

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

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

[Cornelia Huck]

On Wed, 10 Jan 2018 11:47:58 +0200
"Michael S. Tsirkin"  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 
> ---
>  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}

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

[Cornelia Huck]

On Wed, 10 Jan 2018 11:47:58 +0200
"Michael S. Tsirkin"  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.
> 
> 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 
> ---
>  content.tex |  36 ++-
>  packed-ring.tex | 668 
> 
>  2 files changed, 701 insertions(+), 3 deletions(-)
>  create mode 100644 packed-ring.tex

Some minor gripes by git am:

.git/rebase-apply/patch:288: trailing whitespace.
Buffer ID is included in the last descriptor in the list.  
.git/rebase-apply/patch:342: trailing whitespace.
are reserved and are ignored by the device. 

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