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Re: [Qemu-devel] [PATCH 3/3] virtio: set ISR on dataplane notifications


From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH 3/3] virtio: set ISR on dataplane notifications
Date: Wed, 16 Nov 2016 22:39:24 +0200

On Wed, Nov 16, 2016 at 03:38:11PM -0500, Paolo Bonzini wrote:
> > > +void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq)
> > > +{
> > > +    if (!virtio_should_notify(vdev, vq)) {
> > > +        return;
> > > +    }
> > > +
> > > +    trace_virtio_notify_irqfd(vdev, vq);
> > > +    virtio_set_isr(vq->vdev, 0x1);
> > 
> > So here, I think we need a comment with parts of
> > the commit log.
> > 
> > /*
> >  * virtio spec 1.0 says ISR bit 0 should be ignored with MSI, but
> >  * windows drivers included in virtio-win 1.8.0 (circa 2015)
> >  * for Windows 8.1 only are incorrectly polling this bit during shutdown
>          ^^^^^^^^^^^^^^^^
> 
> Not sure it's only for Windows 8.1, in fact probably not.

8.1 on shutdown and others on crashdump or hibernation?

> Looks good if you replace this line with
> 
> "are incorrectly polling this bit during crashdump or hibernation"
> 
> Paolo
> 
> >  * in MSI mode, causing a hang if this bit is never updated.
> >  * Next driver release from 2016 fixed this problem, so working around it
> >  * is not a must, but it's easy to do so let's do it here.
> >  *
> >  * Note: it's safe to update ISR from any thread as it was switched
> >  * to an atomic operation.
> >  */
> 
> 
> > 
> > 
> > 
> > > +    event_notifier_set(&vq->guest_notifier);
> > > +}
> > > +
> > >  void virtio_notify(VirtIODevice *vdev, VirtQueue *vq)
> > >  {
> > >      if (!virtio_should_notify(vdev, vq)) {
> > > @@ -1990,7 +1994,7 @@ static void
> > > virtio_queue_guest_notifier_read(EventNotifier *n)
> > >  {
> > >      VirtQueue *vq = container_of(n, VirtQueue, guest_notifier);
> > >      if (event_notifier_test_and_clear(n)) {
> > > -        virtio_irq(vq);
> > > +        virtio_notify_vector(vq->vdev, vq->vector);
> > >      }
> > >  }
> > >  
> > > diff --git a/include/hw/virtio/virtio-scsi.h
> > > b/include/hw/virtio/virtio-scsi.h
> > > index 9fbc7d7..7375196 100644
> > > --- a/include/hw/virtio/virtio-scsi.h
> > > +++ b/include/hw/virtio/virtio-scsi.h
> > > @@ -137,6 +137,5 @@ void virtio_scsi_push_event(VirtIOSCSI *s, SCSIDevice
> > > *dev,
> > >  void virtio_scsi_dataplane_setup(VirtIOSCSI *s, Error **errp);
> > >  int virtio_scsi_dataplane_start(VirtIODevice *s);
> > >  void virtio_scsi_dataplane_stop(VirtIODevice *s);
> > > -void virtio_scsi_dataplane_notify(VirtIODevice *vdev, VirtIOSCSIReq 
> > > *req);
> > >  
> > >  #endif /* QEMU_VIRTIO_SCSI_H */
> > > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > > index 835b085..ab0e030 100644
> > > --- a/include/hw/virtio/virtio.h
> > > +++ b/include/hw/virtio/virtio.h
> > > @@ -181,6 +181,7 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned
> > > int *in_bytes,
> > >                                 unsigned max_in_bytes, unsigned
> > >                                 max_out_bytes);
> > >  
> > >  bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq);
> > > +void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq);
> > >  void virtio_notify(VirtIODevice *vdev, VirtQueue *vq);
> > >  
> > >  void virtio_save(VirtIODevice *vdev, QEMUFile *f);
> > > @@ -280,7 +281,6 @@ void virtio_queue_host_notifier_read(EventNotifier 
> > > *n);
> > >  void virtio_queue_aio_set_host_notifier_handler(VirtQueue *vq, AioContext
> > >  *ctx,
> > >                                                  void (*fn)(VirtIODevice 
> > > *,
> > >                                                             VirtQueue *));
> > > -void virtio_irq(VirtQueue *vq);
> > >  VirtQueue *virtio_vector_first_queue(VirtIODevice *vdev, uint16_t 
> > > vector);
> > >  VirtQueue *virtio_vector_next_queue(VirtQueue *vq);
> > >  
> > > --
> > > 2.9.3
> > 



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