On 02/22/2010 04:29 PM, Marcelo Tosatti wrote:
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<amit.shah@xxxxxxxxxx>
Signed-off-by: Marcelo Tosatti<mtosatti@xxxxxxxxxx>
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?
I don't understand what this means. ->handle_output() _is_ informing
the device model of new buffers. What more is needed?
Are you concerned about spurious wakeups?
Yes. Also, qemu_notify_event() is an undirected notification (wakes up
all iothreads, and all devices), whereas ->handle_output() is directed
(wakes up exactly what is needed).
What's the underlying problem? A new input buffer has become available,
and we need to re-poll the incoming file descriptor? If so, that's best
done from ->handle_output() (either by waking the iothread or calling
read() itself and perhaps receiving -EAGAIN).
--
error compiling committee.c: too many arguments to function
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