Re: [virtio-dev] [PATCH v3] VIRTIO_F_IO_BARRIER: use I/O barriers in driver

[Tiwei Bie <tiwei.bie@intel.com>]

On Thu, May 10, 2018 at 11:41:26PM +0800, Tiwei Bie wrote:
> There will be hardware virtio devices in the future, which
> require drivers to use the barriers suitable for I/O devices,
> compared with software virtio devices which just require
> drivers to use the barriers suitable for CPU cores.
> 
> 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 devices.
> 
> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

I have opened an issue for this:

Fixes: https://github.com/oasis-tcs/virtio-spec/issues/10

Please start the voting. Thanks!

Best regards,
Tiwei Bie

> ---
> v2 -> v3:
> - Update the feature bits allocation (Stefan);
> 
> v1 -> v2:
> - Rebase to the latest spec (MST);
> - Use a smaller textwidth (according to _vimrc);
> 
> RFC -> v1:
> - Use plural (Stefan);
> - Add more details (Stefan);
> 
>  content.tex | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/content.tex b/content.tex
> index 7a92cb1..95c243f 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -95,10 +95,10 @@ Feature bits are allocated as follows:
>  \begin{description}
>  \item[0 to 23] Feature bits for the specific device type
>  
> -\item[24 to 33] Feature bits reserved for extensions to the queue and
> +\item[24 to 36] Feature bits reserved for extensions to the queue and
>    feature negotiation mechanisms
>  
> -\item[34 and above] Feature bits reserved for future extensions.
> +\item[37 and above] Feature bits reserved for future extensions.
>  \end{description}
>  
>  \begin{note}
> @@ -5348,6 +5348,15 @@ Descriptors} and \ref{sec:Packed Virtqueues / Indirect Flag: Scatter-Gather Supp
>    \item[VIRTIO_F_IN_ORDER(35)] This feature indicates
>    that all buffers are used by the device in the same
>    order in which they have been made available.
> +  \item[VIRTIO_F_IO_BARRIER(36)] This feature indicates
> +  that the device needs the driver to use the barriers
> +  suitable for hardware devices.  Some transports require
> +  barriers to ensure 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 indicates whether
> +  a stronger form of barrier suitable for hardware
> +  devices is necessary.
>  \end{description}
>  
>  \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
> @@ -5363,6 +5372,10 @@ 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 devices.
> +
>  \devicenormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
>  
>  A device MUST offer VIRTIO_F_VERSION_1.  A device MAY fail to operate further
> @@ -5376,6 +5389,9 @@ accepted.
>  If VIRTIO_F_IN_ORDER has been negotiated, a device MUST use
>  buffers in the same order in which they have been available.
>  
> +A device MAY fail to operate further if VIRTIO_F_IO_BARRIER
> +is not accepted.
> +
>  \section{Legacy Interface: Reserved Feature Bits}\label{sec:Reserved Feature Bits / Legacy Interface: Reserved Feature Bits}
>  
>  Transitional devices MAY offer the following:
> -- 
> 2.11.0
> 
> 
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