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authorTiwei Bie <tiwei.bie@intel.com>2018-05-10 23:41:26 +0800
committerMichael S. Tsirkin <mst@redhat.com>2018-05-23 20:34:52 +0300
commit12fe939f1df9482d6134f9ec5ae39ddacc3df426 (patch)
tree0f77676a0eba64be8205e2bead98d8c42ac2138d /content.tex
parent64d1a58f3ffe37ee28c0bc0c34bece8ebd1f6356 (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.tex20
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: