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Subject: [PATCH v3] VIRTIO_F_IO_BARRIER: use I/O barriers in driver
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> --- 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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