Re: [PATCHv6 4/4] virtio_pci: optional MSI-X support

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, May 18, 2009 at 12:30:49AM +0300, Avi Kivity wrote:
> Michael S. Tsirkin wrote:
>> This implements optional MSI-X support in virtio_pci.
>> MSI-X is used whenever the host supports at least 2 MSI-X
>> vectors: 1 for configuration changes and 1 for virtqueues.
>> Per-virtqueue vectors are allocated if enough vectors
>> available.
> 
>
> I'm not sure I understand how the vq -> msi mapping works.  Do we  
> actually support an arbitrary mapping, or just either linear or n:1?

Arbitrary mapping.

> I don't mind the driver being limited, but the device interface should  
> be flexible.  We'll want to deal with limited vector availability soon.

I agree.

The code in qemu lets you specify, for each queue, which MSIX vector you
want to use, or a special value if you don't want signalling. You also
specify which MSIX vector you want to use for config change
notifications, or a special value if you want to e.g. poll.

I think that's as flexible as it gets.

The API within guest is much simpler, but it does not need to be stable.

-- 
MST