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Subject: Re: [PATCH v3] VIRTIO_F_IO_BARRIER: use I/O barriers in driver
On Tue, May 15, 2018 at 03:39:02PM +0300, Michael S. Tsirkin wrote: > 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> > > When you are ready, please open a github issue, then > send Fixes: tag in a response to this mail, asking > to start voting. Got it! Thank you very much! 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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