On Wed, Apr 25, 2018 at 04:23:12PM +0800, Tiwei Bie wrote:
> There will be hardware virtio devices in the future, which
> require drivers to use the barriers suitable for I/O device,
> compared with software virtio devices which just require
> drivers to use the barriers suitable for CPU core.
>
> To fix the ordering issue for hardware virtio devices, add
> a new feature: VIRTIO_F_IO_BARRIER. When negotiated, driver
> will use the barriers suitable for I/O device.
>
> Signed-off-by: Tiwei Bie <>
> ---
> content.tex | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/content.tex b/content.tex
> index ae5fa4c..f24e320 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -5445,6 +5445,8 @@ Descriptors} and \ref{sec:Packed Virtqueues / Indirect Flag: Scatter-Gather Supp
> that drivers pass extra data (besides identifying the Virtqueue)
> in their device notifications.
> See \ref{sec:Virtqueues / Driver notifications}~\nameref{sec:Virtqueues / Driver notifications}.
> + \item[VIRTIO_F_IO_BARRIER(37)] This feature indicates that the device
> + needs the driver to use the barriers suitable for hardware device.
s/hardware device/hardware devices/ (plural)
> \end{description}
>
> \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
> @@ -5460,6 +5462,10 @@ addresses to the device.
>
> A driver SHOULD accept VIRTIO_F_RING_PACKED if it is offered.
>
> +A driver SHOULD accept VIRTIO_F_IO_BARRIER if it is offered.
> +If VIRTIO_F_IO_BARRIER has been negotiated, a driver MUST use
> +the barriers suitable for hardware device.
s/hardware device/hardware devices/ (plural)
Please add a little context so the purpose is clear to readers (I
wouldn't be 100% sure what the spec means without more detail):
Some transports require barriers to ensure hardware devices have a
consistent view of memory. When devices are implemented in software a
weaker form of barrier may be sufficient and yield better performance.
This feature bit indicates whether the full hardware barrier is
necessary.
