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Date: Tue, 22 Mar 2016 09:06:32 +0100
From: Cornelia Huck <cornelia.huck@de.ibm.com>
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Subject: Re: [Qemu-devel] [PATCH 0/4] Tweaks around virtio-blk start/stop
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To: Fam Zheng <famz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>, qemu-devel@nongnu.org, tu bo <tubo@linux.vnet.ibm.com>, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Christian Borntraeger <borntraeger@de.ibm.com>

On Tue, 22 Mar 2016 07:45:19 +0800
Fam Zheng <famz@redhat.com> wrote:

> On Mon, 03/21 14:02, Cornelia Huck wrote:
> > On Mon, 21 Mar 2016 20:45:27 +0800
> > Fam Zheng <famz@redhat.com> wrote:
> > 
> > > On Mon, 03/21 12:15, Cornelia Huck wrote:
> > > > On Mon, 21 Mar 2016 18:57:18 +0800
> > > > Fam Zheng <famz@redhat.com> wrote:
> > > > 
> > > > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > > > > index 08275a9..47f8043 100644
> > > > > --- a/hw/virtio/virtio.c
> > > > > +++ b/hw/virtio/virtio.c
> > > > > @@ -1098,7 +1098,14 @@ void virtio_queue_notify_vq(VirtQueue *vq)
> > > > > 
> > > > >  void virtio_queue_notify(VirtIODevice *vdev, int n)
> > > > >  {
> > > > > -    virtio_queue_notify_vq(&vdev->vq[n]);
> > > > > +    VirtQueue *vq = &vdev->vq[n];
> > > > > +    EventNotifier *n;
> > > > > +    n = virtio_queue_get_host_notifier(vq);
> > > > > +    if (n) {
> > > > 
> > > > Isn't that always true, even if the notifier has not been setup?
> > > 
> > > You are right, this doesn't make a correct fix. But we can still do a quick
> > > test with this as the else branch should never be used with ioeventfd=on. Am I
> > > right?
> > > 
> > > Fam
> > 
> > Won't we come through here for the very first kick, when we haven't
> > registered the ioeventfd with the kernel yet?
> > 
> 
> The ioeventfd in virtio-ccw is registered in the main loop when
> VIRTIO_CONFIG_S_DRIVER_OK is set, so I think the first kick is okay.

You're right, for well-behaved drivers this will be done from
set_status, so for testing that's fine.