Re: [Qemu-devel] [PATCH v2 1/2] virtio-net: enable configurable tx queue size

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jun 16, 2017 at 06:48:38PM +0800, Wei Wang wrote:
> This patch enables the virtio-net tx queue size to be configurable
> between 256 (the default queue size) and 1024 by the user when the
> vhost-user backend is used.
> 
> Currently, the maximum tx queue size for other backends is 512 due
> to the following limitations:
> - QEMU backend: the QEMU backend implementation in some cases may
> send 1024+1 iovs to writev.
> - Vhost_net backend: there are possibilities that the guest sends
> a vring_desc of memory which corsses a MemoryRegion thereby
> generating more than 1024 iovs in total after translattion from
> guest-physical address in the backend.
> 
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> ---
>  hw/net/virtio-net.c            | 46 ++++++++++++++++++++++++++++++++++--------
>  include/hw/virtio/virtio-net.h |  1 +
>  2 files changed, 39 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 7d091c9..e1a08fd 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -33,8 +33,11 @@
>  
>  /* previously fixed value */
>  #define VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE 256
> +#define VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE 256
> +
>  /* for now, only allow larger queues; with virtio-1, guest can downsize */
>  #define VIRTIO_NET_RX_QUEUE_MIN_SIZE VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE
> +#define VIRTIO_NET_TX_QUEUE_MIN_SIZE VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE
>  
>  /*
>   * Calculate the number of bytes up to and including the given 'field' of
> @@ -1491,18 +1494,33 @@ static void virtio_net_tx_bh(void *opaque)
>  static void virtio_net_add_queue(VirtIONet *n, int index)
>  {
>      VirtIODevice *vdev = VIRTIO_DEVICE(n);
> +    NetClientState *nc = qemu_get_queue(n->nic);
>  
>      n->vqs[index].rx_vq = virtio_add_queue(vdev, n->net_conf.rx_queue_size,
>                                             virtio_net_handle_rx);
> +
> +    /*
> +     * Currently, backends other than vhost-user don't support 1024 queue
> +     * size.
> +     */
> +    if (n->net_conf.tx_queue_size == VIRTQUEUE_MAX_SIZE &&
> +        nc->peer->info->type != NET_CLIENT_DRIVER_VHOST_USER) {
> +        fprintf(stderr, "warning: %s: queue size %d not supported\n",
> +                __func__, n->net_conf.tx_queue_size);

OK but it's best to avoid fprintfs. Queue size is easy to see so
I don't think we need it. I've dropped this from the patch for now,
feel free to send a separate patch re-adding this.

> +        n->net_conf.tx_queue_size = VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE;
> +    }
> +
>      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);
> +            virtio_add_queue(vdev, n->net_conf.tx_queue_size,
> +                             virtio_net_handle_tx_timer);
>          n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
>                                                virtio_net_tx_timer,
>                                                &n->vqs[index]);
>      } else {
>          n->vqs[index].tx_vq =
> -            virtio_add_queue(vdev, 256, virtio_net_handle_tx_bh);
> +            virtio_add_queue(vdev, n->net_conf.tx_queue_size,
> +                             virtio_net_handle_tx_bh);
>          n->vqs[index].tx_bh = qemu_bh_new(virtio_net_tx_bh, &n->vqs[index]);
>      }
>  
> @@ -1910,6 +1928,17 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
>          return;
>      }
>  
> +    if (n->net_conf.tx_queue_size < VIRTIO_NET_TX_QUEUE_MIN_SIZE ||
> +        n->net_conf.tx_queue_size > VIRTQUEUE_MAX_SIZE ||
> +        !is_power_of_2(n->net_conf.tx_queue_size)) {
> +        error_setg(errp, "Invalid tx_queue_size (= %" PRIu16 "), "
> +                   "must be a power of 2 between %d and %d",
> +                   n->net_conf.tx_queue_size, VIRTIO_NET_TX_QUEUE_MIN_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 "), "
> @@ -1930,17 +1959,11 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
>          error_report("Defaulting to \"bh\"");
>      }
>  
> -    for (i = 0; i < n->max_queues; i++) {
> -        virtio_net_add_queue(n, i);
> -    }
> -
> -    n->ctrl_vq = virtio_add_queue(vdev, 64, virtio_net_handle_ctrl);
>      qemu_macaddr_default_if_unset(&n->nic_conf.macaddr);
>      memcpy(&n->mac[0], &n->nic_conf.macaddr, sizeof(n->mac));
>      n->status = VIRTIO_NET_S_LINK_UP;
>      n->announce_timer = timer_new_ms(QEMU_CLOCK_VIRTUAL,
>                                       virtio_net_announce_timer, n);
> -
>      if (n->netclient_type) {
>          /*
>           * Happen when virtio_net_set_netclient_name has been called.
> @@ -1952,6 +1975,11 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
>                                object_get_typename(OBJECT(dev)), dev->id, n);
>      }
>  
> +    for (i = 0; i < n->max_queues; i++) {
> +        virtio_net_add_queue(n, i);
> +    }
> +    n->ctrl_vq = virtio_add_queue(vdev, 64, virtio_net_handle_ctrl);
> +
>      peer_test_vnet_hdr(n);
>      if (peer_has_vnet_hdr(n)) {
>          for (i = 0; i < n->max_queues; i++) {
> @@ -2089,6 +2117,8 @@ static Property virtio_net_properties[] = {
>      DEFINE_PROP_STRING("tx", VirtIONet, net_conf.tx),
>      DEFINE_PROP_UINT16("rx_queue_size", VirtIONet, net_conf.rx_queue_size,
>                         VIRTIO_NET_RX_QUEUE_DEFAULT_SIZE),
> +    DEFINE_PROP_UINT16("tx_queue_size", VirtIONet, net_conf.tx_queue_size,
> +                       VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE),
>      DEFINE_PROP_UINT16("host_mtu", VirtIONet, net_conf.mtu, 0),
>      DEFINE_PROP_END_OF_LIST(),
>  };
> diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> index 1eec9a2..fd944ba 100644
> --- a/include/hw/virtio/virtio-net.h
> +++ b/include/hw/virtio/virtio-net.h
> @@ -36,6 +36,7 @@ typedef struct virtio_net_conf
>      int32_t txburst;
>      char *tx;
>      uint16_t rx_queue_size;
> +    uint16_t tx_queue_size;
>      uint16_t mtu;
>  } virtio_net_conf;
>  
> -- 
> 2.7.4