On Mon, Mar 28, 2022 at 9:50 AM jiangheng (H) <[email protected]> wrote: > > > On Sat, 26 Mar 2022 08:13:21 +0000 > > "jiangheng (H)" <[email protected]> wrote: > > > > > Hi all, > > > > > > I tried using the checksum offloads feature in DPDK and it did not see > > working under virtual machine. > > > > > > Port only support TCP checksum and do not support IP checksum: > > > rx_offload_capa = DEV_RX_OFFLOAD_TCP_CKSUM tx_offload_capa = > > > DEV_TX_OFFLOAD_TCP_CKSUM > > > > > > so I config rxmode.offload txmode.offloads as below: > > > rxmode.offloads = DEV_RX_OFFLOAD_TCP_CKSUM txmode.offloads = > > > DEV_TX_OFFLOAD_TCP_CKSUM > > > > > > For TX, I set the following parameters, it works good. > > > mbuf->l2_len = sizeof(*ethhdr) > > > mbuf->l3_len = ip header len > > > mbuf-ol_flags = RTE_MBUF_F_TX_IPV4 | RTE_MBUF_F_TX_TCP_CKSUM > > > > > > Virtio does not support IP checksum offload. Because Virtio passes > > packets to Linux kernel, and Linux kernel does not do IP checksum offload. > > The IP checksum is so trivial it is faster for most things to just do it in > > software; the header is only 20 bytes and it will be in cache. > > > > You should always check device capability before enabling an offload. > > > > > > > For RX, It will execute the following code: > > > In drivers/net/virtio/virtio_rxtx.c virtio_rx_offload function : > > > if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) { > > > hdrlen = hdr_lens.l2_len + hdr_lens.l3_len + hdr_lens.l4_len; > > > if (hdr->csum_start <= hdrlen && l4_supported) { > > > m->ol_flags |= RTE_MBUF_F_RX_L4_CKSUM_NONE; > > > } else { > > > > > > m->ol_flags set to RTE_MBUF_F_RX_L4_CKSUM_NONE, causing the TCP > > RX checksum failed. > > > How do I avoid the above code going into this branch? > > > > > > > If you want TCP checksum offload you have to set > > RTE_ETH_RX_OFFLOAD_TCP_CKSUM in the rxmode when port is > > configured. This will tell virtio to ask the host to do rx offload. Again, > > virtio does not do IP checksum offload and you should always query > > device capability first. > > I have queried device capability and it tell me it supports tcp checksum, not > supports ip checksum. > So I have set RTE_ETH_RX_OFFLOAD_TCP_CKSUM(DEV_RX_OFFLOAD_TCP_CKSUM) flag > when port is configured(use rte_eth_dev_configure function) > But RX checksum still failed in below branch: > drivers/net/virtio/virtio_rxtx.c virtio_rx_offload function: > if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) { > hdrlen = hdr_lens.l2_len + hdr_lens.l3_len + hdr_lens.l4_len; > if (hdr->csum_start <= hdrlen && l4_supported) { > if (hdr->csum_start <= hdrlen && l4_supported) { > m->ol_flags |= RTE_MBUF_F_RX_L4_CKSUM_NONE; > } else { > Hdr->csum_start <= hdrlen, m->ol_flags will set to > RTE_MBUF_F_RX_L4_CKSUM_NONE, causing RX checksum failed.
Could you show the hdr->csum_start and hdrlen value in your test case? IIRC, hdr->csum_start should be hdr_lens.l2_len + hdr_lens.l3_len according to virtio sepc. The virtio spec has an example as follows: ``` For example, consider a partially checksummed TCP (IPv4) packet. It will have a 14 byte ether- net header and 20 byte IP header followed by the TCP header (with the TCP checksum field 16 bytes into that header). csum_start will be 14+20 = 34 (the TCP checksum includes the header), and csum_offset will be 16. ``` -- Thanks, Harold.
