Re: [net-next rfc v7 2/3] virtio_net: multiqueue support
From: Jason Wang <hidden>
Date: 2012-12-03 10:02:18
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kvm, lkml, virtualization
On 12/03/2012 05:47 PM, Michael S. Tsirkin wrote:
On Mon, Dec 03, 2012 at 02:05:27PM +0800, Jason Wang wrote:quoted
On Monday, December 03, 2012 12:34:08 PM Rusty Russell wrote:quoted
Jason Wang [off-list ref] writes:quoted
+static const struct ethtool_ops virtnet_ethtool_ops; + +/* + * Converting between virtqueue no. and kernel tx/rx queue no. + * 0:rx0 1:tx0 2:cvq 3:rx1 4:tx1 ... 2N+1:rxN 2N+2:txN + */ +static int vq2txq(struct virtqueue *vq) +{ + int index = virtqueue_get_queue_index(vq); + return index == 1 ? 0 : (index - 2) / 2; +} + +static int txq2vq(int txq) +{ + return txq ? 2 * txq + 2 : 1; +} + +static int vq2rxq(struct virtqueue *vq) +{ + int index = virtqueue_get_queue_index(vq); + return index ? (index - 1) / 2 : 0; +} + +static int rxq2vq(int rxq) +{ + return rxq ? 2 * rxq + 1 : 0; +} +I thought MST changed the proposed spec to make the control queue always the last one, so this logic becomes trivial.But it may break the support of legacy guest. If we boot a legacy single queue guest on a 2 queue virtio-net device. It may think vq 2 is cvq which is indeed rx1.Legacy guyest support should be handled by host using feature bits in the usual way: host should detect legacy guest by checking the VIRTIO_NET_F_RFS feature. If VIRTIO_NET_F_RFS is acked, cvq is vq max_virtqueue_pairs * 2. If it's not acked, cvq is vq 2.
We could, but we didn't gain much from this. Furthermore, we need also do the dynamic creation/destroying of virtqueues during feature negotiation which seems not supported in qemu now.