On Thu, Sep 24, 2020 at 11:21:01AM +0800, Jason Wang wrote: > This series tries to add the support for control virtqueue in vDPA. Please include documentation for both driver authors and vhost-vdpa ioctl users. vhost-vdpa ioctls are only documented with a single sentence. Please add full information on arguments, return values, and a high-level explanation of the feature (like this cover letter) to introduce the API. What is the policy for using virtqueue groups? My guess is: 1. virtio_vdpa simply enables all virtqueue groups. 2. vhost_vdpa relies on userspace policy on how to use virtqueue groups. Are the semantics of virtqueue groups documented somewhere so userspace knows what to do? If a vDPA driver author decides to create N virtqueue groups, N/2 virtqueue groups, or just 1 virtqueue group, how will userspace know what to do? Maybe a document is needed to describe the recommended device-specific virtqueue groups that vDPA drivers should implement (e.g. "put the net control vq into its own virtqueue group")? This could become messy with guidelines. For example, drivers might be shipped that aren't usable for certain use cases just because the author didn't know that a certain virtqueue grouping is advantageous. BTW I like how general this feature is. It seems to allow vDPA devices to be split into sub-devices for further passthrough. Who will write the first vDPA-on-vDPA driver? :) Stefan
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