[Qemu-devel] Re: [patch uq/master 1/2] virtio-pci: wake up iothread on VIRTIO_PCI_QUEUE_NOTIFY

[Marcelo Tosatti]

On Mon, Feb 22, 2010 at 04:20:52PM +0200, Avi Kivity wrote:
> On 02/22/2010 03:59 PM, Marcelo Tosatti wrote:
> >VIRTIO_PCI_QUEUE_NOTIFY is used to inform availability of new buffers,
> >so wakeup the iothread to process that information immediately.
> >
> >Reported-by: Amit Shah<address@hidden>
> >Signed-off-by: Marcelo Tosatti<address@hidden>
> >
> >Index: qemu/hw/virtio-pci.c
> >===================================================================
> >--- qemu.orig/hw/virtio-pci.c
> >+++ qemu/hw/virtio-pci.c
> >@@ -204,6 +204,7 @@ static void virtio_ioport_write(void *op
> >          break;
> >      case VIRTIO_PCI_QUEUE_NOTIFY:
> >          virtio_queue_notify(vdev, val);
> >+        qemu_notify_event();
> >          break;
> 
> virtio_queue_notify() will call ->handle_output(), which should
> either do what's needed to be done, or wake up some iothread itself.

kick is used to inform either output processing, in which case
->handle_output() does what its supposed to.

But its also used to inform availability of new buffers, which is common
to all virtio devices. So what is the point pushing this to
->handle_output?

Are you concerned about spurious wakeups?