On 07/29/2012 11:44 AM, Michael S. Tsirkin wrote:

On Sat, Jul 21, 2012 at 02:02:58PM +0200, Sasha Levin wrote:

quoted

On 07/20/2012 03:40 PM, Michael S. Tsirkin wrote:

quoted

quoted

-	err = init_vqs(vi);

quoted

+	if (virtio_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ))
+		vi->has_cvq = true;
+

How about we disable multiqueue if there's no cvq?
Will make logic a bit simpler, won't it?

multiqueues don't really depend on cvq. Does this added complexity really justifies adding an artificial limit?

Well !cvq support is a legacy feature: the reason we support it
in driver is to avoid breaking on old hosts. Adding more code to that
path just doesn't make much sense since old hosts won't have mq.

Is it really a legacy feature? The spec suggests that its an optional queue which is not necessary for the operation of the device.

Which is why we never implemented it in lkvm - we weren't interested in any of the features it provided at that time and we could provide high performance with vhost support even without it.