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Subject: [PATCH v1] 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> --- RFC -> v1: - Use plural (Stefan); - Add more details (Stefan); content.tex | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/content.tex b/content.tex index ae5fa4c..a1c09c4 100644 --- a/content.tex +++ b/content.tex @@ -5445,6 +5445,13 @@ 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 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} @@ -5460,6 +5467,10 @@ 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 @@ -5473,6 +5484,9 @@ 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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