RE: [PATCH 6/6] net/vhost: perform SW checksum in Tx path

["Ma, WenwuX" <wenwux.ma@intel.com>]

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: 2022年5月5日 18:27
> To: dev@dpdk.org; jasowang@redhat.com; Xia, Chenbo
> <chenbo.xia@intel.com>; david.marchand@redhat.com;
> olivier.matz@6wind.com
> Cc: stable@dpdk.org; Maxime Coquelin <maxime.coquelin@redhat.com>
> Subject: [PATCH 6/6] net/vhost: perform SW checksum in Tx path
> 
> Virtio specification supports guest checksum offloading for L4, which is
> enabled with VIRTIO_NET_F_GUEST_CSUM feature negotiation. However,
> the Vhost PMD does not advertise Tx checksum offload capabilities.
> 
> Advertising these offload capabilities at the ethdev level is not enough,
> because we could still end-up with the application enabling these offloads
> while the guest not negotiating it.
> 
> This patch advertizes the Tx checksum offload capabilities, and introduces a
> compatibility layer to cover the case VIRTIO_NET_F_GUEST_CSUM has not
> been negotiated but the application does configure the Tx checksum
> offloads. This function performs the L4 Tx checksum in SW for UDP and TCP.
> Compared to Rx SW checksum, the Tx SW checksum function needs to
> compute the pseudo-header checksum, as we cannot knwo whether it was
> done before.
> 
> This patch does not advertize SCTP checksum offloading capability for now,
> but it could be handled later if the need arises.

In virtio_enqueue_offload(), if RTE_MBUF_F_TX_IP_CKSUM is set, we will
performs the L3 Tx checksum, why do not we advertise IPV4 checksum offloading capability?
Will we advertise it later?

> 
> Reported-by: Jason Wang <jasowang@redhat.com>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>  drivers/net/vhost/rte_eth_vhost.c | 62
> +++++++++++++++++++++++++++++++
>  1 file changed, 62 insertions(+)
> 
> diff --git a/drivers/net/vhost/rte_eth_vhost.c
> b/drivers/net/vhost/rte_eth_vhost.c
> index d5303f7368..52a802de05 100644
> --- a/drivers/net/vhost/rte_eth_vhost.c
> +++ b/drivers/net/vhost/rte_eth_vhost.c
> @@ -114,6 +114,7 @@ struct pmd_internal {
>  	rte_atomic32_t started;
>  	bool vlan_strip;
>  	bool rx_sw_csum;
> +	bool tx_sw_csum;
>  };
> 
>  struct internal_list {
> @@ -370,8 +371,10 @@ vhost_dev_csum_configure(struct rte_eth_dev
> *eth_dev)  {
>  	struct pmd_internal *internal = eth_dev->data->dev_private;
>  	const struct rte_eth_rxmode *rxmode = &eth_dev->data-
> >dev_conf.rxmode;
> +	const struct rte_eth_txmode *txmode = &eth_dev->data-
> >dev_conf.txmode;
> 
>  	internal->rx_sw_csum = false;
> +	internal->tx_sw_csum = false;
> 
>  	/* SW checksum is not compatible with legacy mode */
>  	if (!(internal->flags &
> RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS))
> @@ -384,6 +387,56 @@ vhost_dev_csum_configure(struct rte_eth_dev
> *eth_dev)
>  			internal->rx_sw_csum = true;
>  		}
>  	}
> +
> +	if (!(internal->features & (1ULL << VIRTIO_NET_F_GUEST_CSUM))) {
> +		if (txmode->offloads &
> +				(RTE_ETH_TX_OFFLOAD_UDP_CKSUM |
> RTE_ETH_TX_OFFLOAD_TCP_CKSUM)) {
> +			VHOST_LOG(NOTICE, "Tx csum will be done in SW,
> may impact performance.");
> +			internal->tx_sw_csum = true;
> +		}
> +	}
> +}
> +
> +static void
> +vhost_dev_tx_sw_csum(struct rte_mbuf *mbuf) {
> +	uint32_t hdr_len;
> +	uint16_t csum = 0, csum_offset;
> +
> +	switch (mbuf->ol_flags & RTE_MBUF_F_TX_L4_MASK) {
> +	case RTE_MBUF_F_TX_L4_NO_CKSUM:
> +		return;
> +	case RTE_MBUF_F_TX_TCP_CKSUM:
> +		csum_offset = offsetof(struct rte_tcp_hdr, cksum);
> +		break;
> +	case RTE_MBUF_F_TX_UDP_CKSUM:
> +		csum_offset = offsetof(struct rte_udp_hdr, dgram_cksum);
> +		break;
> +	default:
> +		/* Unsupported packet type. */
> +		return;
> +	}
> +
> +	hdr_len = mbuf->l2_len + mbuf->l3_len;
> +	csum_offset += hdr_len;
> +
> +	/* Prepare the pseudo-header checksum */
> +	if (rte_net_intel_cksum_prepare(mbuf) < 0)
> +		return;
> +
> +	if (rte_raw_cksum_mbuf(mbuf, hdr_len,
> rte_pktmbuf_pkt_len(mbuf) - hdr_len, &csum) < 0)
> +		return;
> +
> +	csum = ~csum;
> +	/* See RFC768 */
> +	if (unlikely((mbuf->packet_type & RTE_PTYPE_L4_UDP) && csum ==
> 0))
> +		csum = 0xffff;
> +
> +	if (rte_pktmbuf_data_len(mbuf) >= csum_offset + 1)
> +		*rte_pktmbuf_mtod_offset(mbuf, uint16_t *, csum_offset)
> = csum;
> +
> +	mbuf->ol_flags &= ~RTE_MBUF_F_TX_L4_MASK;
> +	mbuf->ol_flags |= RTE_MBUF_F_TX_L4_NO_CKSUM;
>  }
> 
>  static void
> @@ -513,6 +566,10 @@ eth_vhost_tx(void *q, struct rte_mbuf **bufs,
> uint16_t nb_bufs)
>  			}
>  		}
> 
> +		if (r->internal->tx_sw_csum)
> +			vhost_dev_tx_sw_csum(m);
> +
> +
>  		bufs[nb_send] = m;
>  		++nb_send;
>  	}
> @@ -1359,6 +1416,11 @@ eth_dev_info(struct rte_eth_dev *dev,
> 
>  	dev_info->tx_offload_capa = RTE_ETH_TX_OFFLOAD_MULTI_SEGS |
>  				RTE_ETH_TX_OFFLOAD_VLAN_INSERT;
> +	if (internal->flags & RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS)
> {
> +		dev_info->tx_offload_capa |=
> RTE_ETH_TX_OFFLOAD_UDP_CKSUM |
> +			RTE_ETH_TX_OFFLOAD_TCP_CKSUM;
> +	}
> +
>  	dev_info->rx_offload_capa = RTE_ETH_RX_OFFLOAD_VLAN_STRIP;
>  	if (internal->flags & RTE_VHOST_USER_NET_COMPLIANT_OL_FLAGS)
> {
>  		dev_info->rx_offload_capa |=
> RTE_ETH_RX_OFFLOAD_UDP_CKSUM |
> --
> 2.35.1