From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from proxy.6wind.com (host.76.145.23.62.rev.coltfrance.com [62.23.145.76]) by dpdk.org (Postfix) with ESMTP id 8916A6936 for ; Tue, 11 Oct 2016 16:29:54 +0200 (CEST) Received: from [10.16.0.195] (unknown [10.16.0.195]) by proxy.6wind.com (Postfix) with ESMTP id 54C2F272AD; Tue, 11 Oct 2016 16:29:54 +0200 (CEST) To: Maxime Coquelin , dev@dpdk.org, yuanhan.liu@linux.intel.com References: <1469088510-7552-1-git-send-email-olivier.matz@6wind.com> <1475485223-30566-1-git-send-email-olivier.matz@6wind.com> <1475485223-30566-10-git-send-email-olivier.matz@6wind.com> <9a1ef865-7bff-33cd-5d6e-01ff9e4b1b5a@redhat.com> Cc: konstantin.ananyev@intel.com, sugesh.chandran@intel.com, bruce.richardson@intel.com, jianfeng.tan@intel.com, helin.zhang@intel.com, adrien.mazarguil@6wind.com, stephen@networkplumber.org, dprovan@bivio.net, xiao.w.wang@intel.com From: Olivier MATZ Message-ID: <57FCF75E.3090205@6wind.com> Date: Tue, 11 Oct 2016 16:29:50 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.6.0 MIME-Version: 1.0 In-Reply-To: <9a1ef865-7bff-33cd-5d6e-01ff9e4b1b5a@redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [dpdk-dev] [PATCH v2 09/12] virtio: add Rx checksum offload support X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 11 Oct 2016 14:29:54 -0000 On 10/11/2016 04:04 PM, Maxime Coquelin wrote: >> +/* Optionally fill offload information in structure */ >> +static int >> +virtio_rx_offload(struct rte_mbuf *m, struct virtio_net_hdr *hdr) >> +{ >> + struct rte_net_hdr_lens hdr_lens; >> + uint32_t hdrlen, ptype; >> + int l4_supported = 0; >> + >> + /* nothing to do */ >> + if (hdr->flags == 0 && hdr->gso_type == VIRTIO_NET_HDR_GSO_NONE) >> + return 0; >> + >> + m->ol_flags |= PKT_RX_IP_CKSUM_UNKNOWN; >> + >> + ptype = rte_net_get_ptype(m, &hdr_lens, RTE_PTYPE_ALL_MASK); >> + m->packet_type = ptype; >> + if ((ptype & RTE_PTYPE_L4_MASK) == RTE_PTYPE_L4_TCP || >> + (ptype & RTE_PTYPE_L4_MASK) == RTE_PTYPE_L4_UDP || >> + (ptype & RTE_PTYPE_L4_MASK) == RTE_PTYPE_L4_SCTP) >> + l4_supported = 1; >> + >> + 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 |= PKT_RX_L4_CKSUM_NONE; >> + } else { >> + /* Unknown proto or tunnel, do sw cksum. We can assume >> + * the cksum field is in the first segment since the >> + * buffers we provided to the host are large enough. >> + * In case of SCTP, this will be wrong since it's a CRC >> + * but there's nothing we can do. >> + */ >> + uint16_t csum, off; >> + >> + csum = rte_raw_cksum_mbuf(m, hdr->csum_start, >> + rte_pktmbuf_pkt_len(m) - hdr->csum_start); >> + if (csum != 0xffff) > Why don't we do the 1-complement if 0xffff? This was modified after a comment from Xiao. In checksum arithmetic (ones' complement), there are 2 equivalent ways to say the checksum is 0: 0xffff (0-), and 0x0000 (0+). Some protocols like UDP use this to differentiate between 0xffff (packet checksum is 0) and 0x0000 (packet checksum is not calculated). Here, we want to avoid to set a checksum to 0, in case it would mean no checksum for UDP packets. Instead, it is set to 0xffff, which is also a valid checksum for this packet. Regards, Olivier