Re: [Qemu-devel] [PULL 01/21] virtio-net: enable configurable tx queue size

[Wei Wang <wei.w.wang@intel.com>]

On 07/04/2017 03:44 AM, Michael S. Tsirkin wrote:
> From: Wei Wang <wei.w.wang@intel.com>
>
> 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 crosses a MemoryRegion thereby
> generating more than 1024 iovs after translation from guest-physical
> address in the backend.
>
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>   include/hw/virtio/virtio-net.h |  1 +
>   hw/net/virtio-net.c            | 32 ++++++++++++++++++++++++++++++--
>   2 files changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> index 602b486..b81b6a4 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;
>   
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 91eddaf..a1fc0db 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -34,8 +34,11 @@
>   
>   /* 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
> @@ -1508,15 +1511,18 @@ static void virtio_net_add_queue(VirtIONet *n, int index)
>   
>       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);
> +            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]);
>       }
>   
> @@ -1927,6 +1933,17 @@ 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 "), "
> @@ -1947,6 +1964,15 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
>           error_report("Defaulting to \"bh\"");
>       }
>   
> +    /*
> +     * Currently, backends other than vhost-user don't support 1024 queue
> +     * size.
> +     */
> +    if (n->net_conf.tx_queue_size == VIRTQUEUE_MAX_SIZE &&
> +        n->nic_conf.peers.ncs[0]->info->type != NET_CLIENT_DRIVER_VHOST_USER) {
> +        n->net_conf.tx_queue_size = VIRTIO_NET_TX_QUEUE_DEFAULT_SIZE;
> +    }
> +
>       for (i = 0; i < n->max_queues; i++) {
>           virtio_net_add_queue(n, i);
>       }
> @@ -2106,6 +2132,8 @@ 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_BOOL("x-mtu-bypass-backend", VirtIONet, mtu_bypass_backend,
>                        true),

Btw, users also expect the support of configuring the tx queue size could
be added to libvirt soon.

Best,
Wei