RE: [PATCH v2 6/6] net/vhost: perform SW checksum in Tx path

["Xia, Chenbo" <chenbo.xia@intel.com>]

+Cheng for review

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Wednesday, June 8, 2022 8:50 PM
> To: dev@dpdk.org; jasowang@redhat.com; Xia, Chenbo <chenbo.xia@intel.com>;
> david.marchand@redhat.com; Matz, Olivier <olivier.matz@6wind.com>; Ma,
> WenwuX <wenwux.ma@intel.com>; Zhang, Yuying <yuying.zhang@intel.com>;
> Singh, Aman Deep <aman.deep.singh@intel.com>
> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
> Subject: [PATCH v2 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 advertises 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
> know whether it was done before.
> 
> This patch does not advertise SCTP checksum offloading
> capability for now, but it could be handled later if the
> need arises.
> 
> 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 42f0d52ebc..d75d256040 100644
> --- a/drivers/net/vhost/rte_eth_vhost.c
> +++ b/drivers/net/vhost/rte_eth_vhost.c
> @@ -92,6 +92,7 @@ struct pmd_internal {
>  	rte_atomic32_t started;
>  	bool vlan_strip;
>  	bool rx_sw_csum;
> +	bool tx_sw_csum;
>  };
> 
>  struct internal_list {
> @@ -283,8 +284,10 @@ 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))
> @@ -297,6 +300,56 @@ 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
> @@ -423,6 +476,10 @@ 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;
>  	}
> @@ -1267,6 +1324,11 @@ 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 |
> --
> 2.35.3