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Type: Bug
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Status: Deferred
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Priority: Major
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Resolution: Unresolved
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Affects Version/s: virtio 1.1 cs01
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Fix Version/s: None
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Labels:None
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Environment:
"Savir, Gil" <gil.savir@intel.com>
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Proposal:
If VIRTIO_F_EVENT_IDX feature bit is negotiated, then Available Buffer
Notification Suppression mechanism used is avail event (not flags).
The spec (both v1.0 / v1.1-draft) states that the device MAY use this mechanism
(Paragraph 2.4.9.2 / 2.6.10.2 respectively).
This statement implies that the device may choose not to use this suppression
mechanism (even if VIRTIO_F_EVENT_IDX was negotiated).
However – there’s no way for the device to inform the driver that he is not
using avail_event.
As consequence, since there will be a default value in avail_event (probably
0x0), then the driver will always assume that it has to send notify “once-per
ring”.
This will render performance futile, or force the device to actively update
avail_event.