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Subject: Re: [virtio-dev] [PATCH v1] VIRTIO_F_IO_BARRIER: use I/O barriers in driver




On 2018年04月28日 11:22, Jason Wang wrote:


On 2018年04月28日 11:19, Tiwei Bie wrote:
On Sat, Apr 28, 2018 at 11:01:55AM +0800, Jason Wang wrote:
On 2018年04月28日 10:23, 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>
---
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.
Users may ask what the specific kinds of barrier here (e.g mmio barrier or
dma barrier). Do we need to clarify that?
IMO it's very obvious that we need all types of barriers used
in the driver should be able to work with hardware devices.

Best regards,
Tiwei Bie


Just in case I do not miss anything, is mmio barrier really needed? I believe what we need is on dma barrier here.

Thanks


Ok, I think I get your meaning here. Driver should choose to use appropriate barriers though mmio barriers is not necessary for current virito. So it looks fine to me.

Thanks




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