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 6417058C5 for ; Thu, 13 Oct 2016 16:02:54 +0200 (CEST) Received: from [10.16.0.195] (unknown [10.16.0.195]) by proxy.6wind.com (Postfix) with ESMTP id BF1A22018B; Thu, 13 Oct 2016 16:02:51 +0200 (CEST) To: Yuanhan Liu References: <1475485223-30566-1-git-send-email-olivier.matz@6wind.com> <1475485223-30566-13-git-send-email-olivier.matz@6wind.com> <20161013081839.GT16751@yliu-dev.sh.intel.com> Cc: dev@dpdk.org, 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: <57FF9409.2090205@6wind.com> Date: Thu, 13 Oct 2016 16:02:49 +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: <20161013081839.GT16751@yliu-dev.sh.intel.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [dpdk-dev] [PATCH v2 12/12] virtio: add Tso 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: Thu, 13 Oct 2016 14:02:54 -0000 On 10/13/2016 10:18 AM, Yuanhan Liu wrote: > On Mon, Oct 03, 2016 at 11:00:23AM +0200, Olivier Matz wrote: >> +/* When doing TSO, the IP length is not included in the pseudo header >> + * checksum of the packet given to the PMD, but for virtio it is >> + * expected. >> + */ >> +static void >> +virtio_tso_fix_cksum(struct rte_mbuf *m) >> +{ >> + /* common case: header is not fragmented */ >> + if (likely(rte_pktmbuf_data_len(m) >= m->l2_len + m->l3_len + >> + m->l4_len)) { > ... >> + /* replace it in the packet */ >> + th->cksum = new_cksum; >> + } else { > ... >> + /* replace it in the packet */ >> + *rte_pktmbuf_mtod_offset(m, uint8_t *, >> + m->l2_len + m->l3_len + 16) = new_cksum.u8[0]; >> + *rte_pktmbuf_mtod_offset(m, uint8_t *, >> + m->l2_len + m->l3_len + 17) = new_cksum.u8[1]; >> + } > > The tcp header will always be in the mbuf, right? Otherwise, you can't > update the cksum field here. What's the point of introducing the "else > clause" then? Sorry, I don't see the problem you're pointing out here. What I want to solve here is to support the cases where the mbuf is segmented in the middle of the network header (which is probably a rare case). In the "else" part, I only access the mbuf byte by byte using the rte_pktmbuf_mtod_offset() accessor. An alternative would have been to copy the header in a linear buffer, fix the checksum, then copy it again in the packet, but there is no mbuf helpers to do these copies for now. Regards, Olivier