diff options
| author | Tiwei Bie <tiwei.bie@intel.com> | 2018-05-10 23:41:26 +0800 |
|---|---|---|
| committer | Michael S. Tsirkin <mst@redhat.com> | 2018-05-23 20:34:52 +0300 |
| commit | 12fe939f1df9482d6134f9ec5ae39ddacc3df426 (patch) | |
| tree | 0f77676a0eba64be8205e2bead98d8c42ac2138d /content.tex | |
| parent | 64d1a58f3ffe37ee28c0bc0c34bece8ebd1f6356 (diff) | |
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.
Fixes: https://github.com/oasis-tcs/virtio-spec/issues/10
Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Diffstat (limited to 'content.tex')
| -rw-r--r-- | content.tex | 20 |
1 files changed, 18 insertions, 2 deletions
diff --git a/content.tex b/content.tex index 110ab70..c4b3b5c 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} @@ -5356,6 +5356,15 @@ 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} @@ -5371,6 +5380,10 @@ 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 @@ -5384,6 +5397,9 @@ 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: |