Re: [Qemu-devel] Qemu-devel Digest, Vol 149, Issue 266

[Marcel Apfelbaum]

On 08/13/2015 08:32 AM, Ouyang, Changchun wrote:
> > -----Original Message-----
> > Date: Wed, 12 Aug 2015 14:15:54 +0300
> > From: "Michael S. Tsirkin" <address@hidden>
> > To: Marcel Apfelbaum <address@hidden>
> > Cc: address@hidden
> > Subject: Re: [Qemu-devel] [PATCH] virtio/vhost: drop unnecessary
> >         VHOST_SET_VRING call
> > Message-ID: <address@hidden>
> > Content-Type: text/plain; charset=us-ascii
> >
> > On Wed, Aug 12, 2015 at 02:10:56PM +0300, Marcel Apfelbaum wrote:
> > > On 08/12/2015 01:34 PM, Michael S. Tsirkin wrote:
> > > > On Wed, Aug 12, 2015 at 01:19:51PM +0300, Marcel Apfelbaum wrote:
> > > > > No need to send VHOST_SET_VRING_CALL to backend before the
> > > > > negotiation with the guest is finished.
> > > > >
> > > > > Signed-off-by: Marcel Apfelbaum <address@hidden>
> > > >
> > > > Well - we do need to set it to the masked notifier initially to avoid
> > > > losing events.  You can't just drop it - need to move this call
> > > > somewhere else.
>
> Agree with m.s.t.
> We could not drop it.
> Vhost-user multi queue also need this.
I'll try to call it a little bit later instead of dropping it.

Thanks,
Marcel

> > > What do we need to set?
> > > I just dropped the call to VHOST_SET_VRING_CALL.
> > >
> > > Thanks,
> > > Marcel
> >
> > We use two eventfds: masked and unmasked one.
> > We switch dynamically dependent on msi mask value.
> > Code assumes we start out masked, so we need to match that.
> >
> >
> > > > > ---
> > > > >   hw/virtio/vhost.c | 13 +------------
> > > > >   1 file changed, 1 insertion(+), 12 deletions(-)
> > > > >
> > > > > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c index
> > > > > 2712c6f..b448542 100644
> > > > > --- a/hw/virtio/vhost.c
> > > > > +++ b/hw/virtio/vhost.c
> > > > > @@ -875,24 +875,13 @@ static void
> > vhost_eventfd_del(MemoryListener
> > > > > *listener,
> > > > >   static int vhost_virtqueue_init(struct vhost_dev *dev,
> > > > >                                   struct vhost_virtqueue *vq, int n)
> > > > >   {
> > > > > -    struct vhost_vring_file file = {
> > > > > -        .index = n,
> > > > > -    };
> > > > >       int r = event_notifier_init(&vq->masked_notifier, 0);
> > > > > +
> > > > >       if (r < 0) {
> > > > >           return r;
> > > > >       }
> > > > >
> > > > > -    file.fd = event_notifier_get_fd(&vq->masked_notifier);
> > > > > -    r = dev->vhost_ops->vhost_call(dev, VHOST_SET_VRING_CALL, &file);
> > > > > -    if (r) {
> > > > > -        r = -errno;
> > > > > -        goto fail_call;
> > > > > -    }
> > > > >       return 0;
> > > > > -fail_call:
> > > > > -    event_notifier_cleanup(&vq->masked_notifier);
> > > > > -    return r;
> > > > >   }
> > > > >
> > > > >   static void vhost_virtqueue_cleanup(struct vhost_virtqueue *vq)
> > > > > --
> > > > > 2.1.0