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

[Jason Wang]

On Fri, Mar 20, 2015 at 7:39 PM, Cornelia Huck 
<address@hidden> wrote:
> On Wed, 18 Mar 2015 17:35:04 +0800
> Jason Wang <address@hidden> 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 <address@hidden>
> >  Signed-off-by: Jason Wang <address@hidden>
> >  ---
> >   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?

Though I don't think it will introduce noticeable overhead. But looks 
like we can do as you suggest. Will do it in next version.

Thanks