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Date: Thu, 9 Feb 2017 13:39:17 +0800
From: Fam Zheng <famz@redhat.com>
Message-ID: <20170209053917.GH22807@lemon.lan>
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Subject: Re: [Qemu-devel] virtio-scsi-pci iothread spins at 100%
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To: Ed Swierk <eswierk@skyportsystems.com>
Cc: qemu-devel@nongnu.org, stefanha@redhat.com

On Wed, 02/08 19:44, Ed Swierk wrote:
> On Wed, Feb 8, 2017 at 6:52 PM, Fam Zheng <famz@redhat.com> wrote:
> > This means virtio-scsi event vq handler is returning true but actually no
> > progress is made. Can you try the following patch to see if it's because a
> > stalled cache of VQ index?
> >
> > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> > index 6365706..7f7ab57 100644
> > --- a/hw/virtio/virtio.c
> > +++ b/hw/virtio/virtio.c
> > @@ -2126,7 +2126,7 @@ static bool virtio_queue_host_notifier_aio_poll(void *opaque)
> >      EventNotifier *n = opaque;
> >      VirtQueue *vq = container_of(n, VirtQueue, host_notifier);
> >
> > -    if (virtio_queue_empty(vq)) {
> > +    if (vring_avail_idx(vq) == vq->last_avail_idx) {
> >          return false;
> >      }
> 
> I tried this change but the behavior is the same, unfortunately.

Hmm, maybe I'm missing something. How about this:

diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index ce19eff..8b23e80 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -754,9 +754,7 @@ out:
 
 void virtio_scsi_handle_event_vq(VirtIOSCSI *s, VirtQueue *vq)
 {
-    if (s->events_dropped) {
-        virtio_scsi_push_event(s, NULL, VIRTIO_SCSI_T_NO_EVENT, 0);
-    }
+    virtio_scsi_push_event(s, NULL, VIRTIO_SCSI_T_NO_EVENT, 0);
 }
 
 static void virtio_scsi_handle_event(VirtIODevice *vdev, VirtQueue *vq)