On Thu, Aug 04, 2016 at 02:16:14AM +0300, Michael S. Tsirkin wrote:
> This allows increasing the rx queue size up to 1024: unlike with tx,
> guests don't put in huge S/G lists into RX so the risk of running into
> the max 1024 limitation due to some off-by-one seems small.
>
> It's helpful for users like OVS-DPDK which don't do any buffering on the
> host - 1K roughly matches 500 entries in tun + 256 in the current rx
> queue, which seems to work reasonably well. We could probably make do
> with ~750 entries but virtio spec limits us to powers of two.
> It might be a good idea to specify an s/g size limit in a future
> version.
>
> It also might be possible to make the queue size smaller down the road, 64
> seems like the minimal value which will still work (as guests seem to
> assume a queue full of 1.5K buffers is enough to process the largest
> incoming packet, which is ~64K). No one actually asked for this, and
> with virtio 1 guests can reduce ring size without need for host
> configuration, so don't bother with this for now.
>
> Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
Forgot to say: this was originally suggested by Patrik Hermansson
<phermans...@gmail.com>
> ---
> include/hw/virtio/virtio-net.h | 1 +
> hw/net/virtio-net.c | 22 +++++++++++++++++++++-
> 2 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> index 91ed97c..0ced975 100644
> --- a/include/hw/virtio/virtio-net.h
> +++ b/include/hw/virtio/virtio-net.h
> @@ -35,6 +35,7 @@ typedef struct virtio_net_conf
> uint32_t txtimer;
> int32_t txburst;
> char *tx;
> + uint16_t rx_queue_size;
> } virtio_net_conf;
>
> /* Maximum packet size we can receive from tap device: header + 64k */
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 01f1351..4e595e9 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -1412,7 +1412,8 @@ static void virtio_net_add_queue(VirtIONet *n, int
> index)
> {
> VirtIODevice *vdev = VIRTIO_DEVICE(n);
>
> - n->vqs[index].rx_vq = virtio_add_queue(vdev, 256, virtio_net_handle_rx);
> + n->vqs[index].rx_vq = virtio_add_queue(vdev, n->net_conf.rx_queue_size,
> + virtio_net_handle_rx);
> if (n->net_conf.tx && !strcmp(n->net_conf.tx, "timer")) {
> n->vqs[index].tx_vq =
> virtio_add_queue(vdev, 256, virtio_net_handle_tx_timer);
> @@ -1716,10 +1717,28 @@ static void virtio_net_device_realize(DeviceState
> *dev, Error **errp)
> VirtIONet *n = VIRTIO_NET(dev);
> NetClientState *nc;
> int i;
> + int min_rx_queue_size;
>
> virtio_net_set_config_size(n, n->host_features);
> virtio_init(vdev, "virtio-net", VIRTIO_ID_NET, n->config_size);
>
> + /*
> + * We set a lower limit on RX queue size to what it always was.
> + * Guests that want a smaller ring can always resize it without
> + * help from us (using virtio 1 and up).
> + */
> + min_rx_queue_size = 256;
> + if (n->net_conf.rx_queue_size < min_rx_queue_size ||
> + n->net_conf.rx_queue_size > VIRTQUEUE_MAX_SIZE ||
> + (n->net_conf.rx_queue_size & (n->net_conf.rx_queue_size - 1))) {
> + error_setg(errp, "Invalid rx_queue_size (= %" PRIu16 "), "
> + "must be a power of 2 between %d and %d.",
> + n->net_conf.rx_queue_size, min_rx_queue_size,
> + VIRTQUEUE_MAX_SIZE);
> + virtio_cleanup(vdev);
> + return;
> + }
> +
> n->max_queues = MAX(n->nic_conf.peers.queues, 1);
> if (n->max_queues * 2 + 1 > VIRTIO_QUEUE_MAX) {
> error_setg(errp, "Invalid number of queues (= %" PRIu32 "), "
> @@ -1880,6 +1899,7 @@ static Property virtio_net_properties[] = {
> TX_TIMER_INTERVAL),
> DEFINE_PROP_INT32("x-txburst", VirtIONet, net_conf.txburst, TX_BURST),
> DEFINE_PROP_STRING("tx", VirtIONet, net_conf.tx),
> + DEFINE_PROP_UINT16("rx_queue_size", VirtIONet, net_conf.rx_queue_size,
> 256),
> DEFINE_PROP_END_OF_LIST(),
> };
>
> --
> MST
