Re: [dpdk-dev] [v4] net/virtio: set offload flag for jumbo frames

[Ilya Maximets <i.maximets@samsung.com>]

On 01.02.2019 13:03, Jens Freimann wrote:
> Port configuration fails because offload flags don't match the expected
> value when max-pkt-len is set to a value that should enable receive port
> offloading but doesn't.
> 
> There are two cases to consider:
> 
> 1. VIRTIO_NET_F_MTU is set. Then we need to check if the requested
>    max-pkt-len fits into the MTU plus header. If yes we set the
>    offload flag.
> 2. VIRTIO_NET_F_MTU is not set. We can set the offload flag.
> 
> Fixes: a4996bd89c42 ("ethdev: new Rx/Tx offloads API")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Jens Freimann <jfreimann@redhat.com>
> ---
> v3->v4:
>  * make use of hw-max_mtu which is calculated during device init. This
>    way we don't have to re-read the mtu from config space again. This
>    is safe because hw->max_mtu is not changed after init.
> 
> v2->v3:
>  * remove unnecessary brackets (Maxime)
>  * fix commit message (David)
> 
> v1->v2:
>  * include virtnet hdr, ethernet header, vlan tag when comparing against
>    max-rx-pkt-len (Maxime)
> 
>  drivers/net/virtio/virtio_ethdev.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
> index 7c4c1df00..4cf91909d 100644
> --- a/drivers/net/virtio/virtio_ethdev.c
> +++ b/drivers/net/virtio/virtio_ethdev.c
> @@ -2351,6 +2351,16 @@ virtio_dev_info_get(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
>  	if ((host_features & tso_mask) == tso_mask)
>  		dev_info->rx_offload_capa |= DEV_RX_OFFLOAD_TCP_LRO;
>  
> +	if (host_features & (1ULL << VIRTIO_NET_F_MTU)) {
> +		uint32_t ether_hdr_len = ETHER_HDR_LEN + VLAN_TAG_LEN +
> +			hw->vtnet_hdr_size;
> +		if (dev->data->dev_conf.rxmode.max_rx_pkt_len <=
> +				hw->max_mtu + ether_hdr_len)
> +			dev_info->rx_offload_capa |= DEV_RX_OFFLOAD_JUMBO_FRAME;
> +	} else {
> +		dev_info->rx_offload_capa |= DEV_RX_OFFLOAD_JUMBO_FRAME;
> +	}
> +

As I wrote for v3, hw->max_mtu already calculated taking VIRTIO_NET_F_MTU
into account. If VIRTIO_NET_F_MTU is not set, hw->max_mtu is equal to
"VIRTIO_MAX_RX_PKTLEN - ETHER_HDR_LEN - VLAN_TAG_LEN - hw->vtnet_hdr_size".
i.e. "hw->max_mtu + ether_hdr_len" equal to VIRTIO_MAX_RX_PKTLEN which is
larger or equal to rxmode.max_rx_pkt_len.
So, there is no need to check for VIRTIO_NET_F_MTU here. You may just perform
same check for both cases.

This doesn't give any performance or so, but will simplify the code.

>  	dev_info->tx_offload_capa = DEV_TX_OFFLOAD_MULTI_SEGS |
>  				    DEV_TX_OFFLOAD_VLAN_INSERT;
>  	if (host_features & (1ULL << VIRTIO_NET_F_CSUM)) {
>