Re: [Qemu-devel] [PATCH V4 14/19] virtio: introduce vector to virtqueues mapping

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Wed, 18 Mar 2015 17:35:04 +0800
Jason Wang <jasowang@redhat.com> wrote:

> Currently we will try to traverse all virtqueues to find a subset that
> using a specific vector. This is sub optimal when we will support
> hundreds or even thousands of virtqueues. So this patch introduces a
> method which could be used by transport to get all virtqueues that
> using a same vector. This is done through QLISTs and the number of
> QLISTs was queried through a transport specific method. When guest
> setting vectors, the virtqueue will be linked and helpers for traverse
> the list was also introduced.
> 
> The first user will be virtio pci which will use this to speed up
> MSI-X masking and unmasking handling.
> 
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  hw/virtio/virtio-pci.c         |  8 ++++++++
>  hw/virtio/virtio.c             | 32 ++++++++++++++++++++++++++++++--
>  include/hw/virtio/virtio-bus.h |  1 +
>  include/hw/virtio/virtio.h     |  3 +++
>  4 files changed, 42 insertions(+), 2 deletions(-)

I'm still not too happy introducing this overhead for all devices when
only pci will make use of it.

Could we perhaps make the queue handling dependant on whether the
transport actually provides the query_nvectors callback?