Re: [PATCH] virtio_net: Enable MSI-X vector for ctrl queue

[Jason Wang]

在 2021/6/18 下午8:38, Michael S. Tsirkin 写道:
> On Fri, Jun 18, 2021 at 04:26:25PM +0900, Keiichi Watanabe wrote:
> > When we use vhost-user backend on the host, MSI-X vector should be set
> > so that the vmm can get an irq FD and send it to the backend device
> > process with vhost-user protocol.
> > Since whether the vector is set for a queue is determined depending on
> > the queue has a callback, this commit sets an empty callback for
> > virtio-net's control queue.
> >
> > Signed-off-by: Keiichi Watanabe <keiichiw@xxxxxxxxxxxx>
> I'm confused by this explanation. If the vmm wants to get
> an interrupt it can do so - why change the guest driver?


+1, it sounds like a bug in the backend or we probably need more context 
here.

Thanks


> > ---
> >   drivers/net/virtio_net.c | 7 ++++++-
> >   1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 11f722460513..002e3695d4b3 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -2696,6 +2696,11 @@ static void virtnet_del_vqs(struct virtnet_info *vi)
> >   	virtnet_free_queues(vi);
> >   }
> >   
> > +static void virtnet_ctrlq_done(struct virtqueue *rvq)
> > +{
> > +	/* Do nothing */
> > +}
> > +
> >   /* How large should a single buffer be so a queue full of these can fit at
> >    * least one full packet?
> >    * Logic below assumes the mergeable buffer header is used.
> > @@ -2748,7 +2753,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
> >   
> >   	/* Parameters for control virtqueue, if any */
> >   	if (vi->has_cvq) {
> > -		callbacks[total_vqs - 1] = NULL;
> > +		callbacks[total_vqs - 1] = virtnet_ctrlq_done;
> >   		names[total_vqs - 1] = "control";
> >   	}
> >   
> > --
> > 2.32.0.288.g62a8d224e6-goog