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    SubjectRe: [net-next RFC V5 4/5] virtio_net: multiqueue support
    On 07/29/2012 11:44 AM, Michael S. Tsirkin wrote:
    > On Sat, Jul 21, 2012 at 02:02:58PM +0200, Sasha Levin wrote:
    >> On 07/20/2012 03:40 PM, Michael S. Tsirkin wrote:
    >>>> - err = init_vqs(vi);
    >>>>> + 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.


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