Re: [dpdk-dev] [PATCH v2 1/2] virtio: fix queue size and number of descriptors

["Ouyang, Changchun" <changchun.ouyang@intel.com>]

> -----Original Message-----
> From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> Sent: Tuesday, July 21, 2015 2:41 AM
> To: Ouyang, Changchun
> Cc: dev@dpdk.org; Stephen Hemminger
> Subject: [PATCH v2 1/2] virtio: fix queue size and number of descriptors
> 
> The virtual queue ring size and the number of slots actually usable are
> separate parameters. In the most common environment (QEMU) the virtual
> queue ring size is 256, but some environments the ring maybe much larger.
> 
> The ring size comes from the host and the driver must use the actual size
> passed.
> 
> The number of descriptors can be either zero to use the whole available ring,
> or some value smaller. This is used to limit the number of mbufs allocated for
> the receive ring. If more descriptors are requested than available the size is
> silently truncated.
> 
> Note: the ring size (from host) must be a power of two, but the number of
> descriptors used can be any size from 1 to the size of the virtual ring.
> 
> Reported-by: Ouyang Changchun <changchun.ouyang@intel.com>
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

Basically ok for this change, so
Acked-by: Changchun Ouyang <changchun.ouyang@intel.com>

> ---
>  drivers/net/virtio/virtio_ethdev.c | 17 ++++-------------
>  1 file changed, 4 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/net/virtio/virtio_ethdev.c
> b/drivers/net/virtio/virtio_ethdev.c
> index 9ca9bb2..d460d89 100644
> --- a/drivers/net/virtio/virtio_ethdev.c
> +++ b/drivers/net/virtio/virtio_ethdev.c
> @@ -276,8 +276,6 @@ int virtio_dev_queue_setup(struct rte_eth_dev *dev,
>  	 */
>  	vq_size = VIRTIO_READ_REG_2(hw, VIRTIO_PCI_QUEUE_NUM);
>  	PMD_INIT_LOG(DEBUG, "vq_size: %d nb_desc:%d", vq_size,
> nb_desc);
> -	if (nb_desc == 0)
> -		nb_desc = vq_size;
>  	if (vq_size == 0) {
>  		PMD_INIT_LOG(ERR, "%s: virtqueue does not exist",
> __func__);
>  		return -EINVAL;
> @@ -288,16 +286,6 @@ int virtio_dev_queue_setup(struct rte_eth_dev
> *dev,
>  		return -EINVAL;
>  	}
> 
> -	if (nb_desc < vq_size) {
> -		if (!rte_is_power_of_2(nb_desc)) {
> -			PMD_INIT_LOG(ERR,
> -				     "nb_desc(%u) size is not powerof 2",
> -				     nb_desc);
> -			return -EINVAL;
> -		}
> -		vq_size = nb_desc;
> -	}
> -
>  	if (queue_type == VTNET_RQ) {
>  		snprintf(vq_name, sizeof(vq_name), "port%d_rvq%d",
>  			dev->data->port_id, queue_idx);
> @@ -325,7 +313,10 @@ int virtio_dev_queue_setup(struct rte_eth_dev
> *dev,
>  	vq->queue_id = queue_idx;
>  	vq->vq_queue_index = vtpci_queue_idx;
>  	vq->vq_nentries = vq_size;
> -	vq->vq_free_cnt = vq_size;
> +
> +	if (nb_desc == 0 || nb_desc > vq_size)
> +		nb_desc = vq_size;
> +	vq->vq_free_cnt = nb_desc;
> 
>  	/*
>  	 * Reserve a memzone for vring elements
> --
> 2.1.4