From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Kavanagh, Mark B" Subject: Re: [PATCH v3 2/5] gso: add TCP/IPv4 GSO support Date: Thu, 14 Sep 2017 08:35:29 +0000 Message-ID: References: <1504598270-60080-1-git-send-email-jiayu.hu@intel.com> <1505184211-36728-1-git-send-email-jiayu.hu@intel.com> <1505184211-36728-3-git-send-email-jiayu.hu@intel.com> <2601191342CEEE43887BDE71AB9772584F249E8E@irsmsx105.ger.corp.intel.com> <20170913024801.GB44293@dpdk15.sh.intel.com> <2601191342CEEE43887BDE71AB9772584F24A622@irsmsx105.ger.corp.intel.com> <2601191342CEEE43887BDE71AB9772584F24A843@irsmsx105.ger.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Cc: "dev@dpdk.org" , "Tan, Jianfeng" To: "Hu, Jiayu" , "Ananyev, Konstantin" Return-path: Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by dpdk.org (Postfix) with ESMTP id D376E2C58 for ; Thu, 14 Sep 2017 10:35:32 +0200 (CEST) In-Reply-To: Content-Language: en-US List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" >From: Hu, Jiayu >Sent: Thursday, September 14, 2017 2:00 AM >To: Ananyev, Konstantin ; Kavanagh, Mark B > >Cc: dev@dpdk.org; Tan, Jianfeng >Subject: RE: [PATCH v3 2/5] gso: add TCP/IPv4 GSO support > >Hi Konstantin, > >> -----Original Message----- >> From: Ananyev, Konstantin >> Sent: Wednesday, September 13, 2017 11:13 PM >> To: Kavanagh, Mark B ; Hu, Jiayu >> >> Cc: dev@dpdk.org; Tan, Jianfeng >> Subject: RE: [PATCH v3 2/5] gso: add TCP/IPv4 GSO support >> >> Hi Mark, >> >> > -----Original Message----- >> > From: Kavanagh, Mark B >> > Sent: Wednesday, September 13, 2017 3:52 PM >> > To: Ananyev, Konstantin ; Hu, Jiayu >> >> > Cc: dev@dpdk.org; Tan, Jianfeng >> > Subject: RE: [PATCH v3 2/5] gso: add TCP/IPv4 GSO support >> > >> > >From: Ananyev, Konstantin >> > >Sent: Wednesday, September 13, 2017 10:38 AM >> > >To: Hu, Jiayu >> > >Cc: dev@dpdk.org; Kavanagh, Mark B ; >> Tan, Jianfeng >> > > >> > >Subject: RE: [PATCH v3 2/5] gso: add TCP/IPv4 GSO support >> > > >> > > >> > > >> > >> > > + >> > >> > > +int >> > >> > > +gso_tcp4_segment(struct rte_mbuf *pkt, >> > >> > > + uint16_t gso_size, >> > >> > > + uint8_t ipid_delta, >> > >> > > + struct rte_mempool *direct_pool, >> > >> > > + struct rte_mempool *indirect_pool, >> > >> > > + struct rte_mbuf **pkts_out, >> > >> > > + uint16_t nb_pkts_out) >> > >> > > +{ >> > >> > > + struct ipv4_hdr *ipv4_hdr; >> > >> > > + uint16_t tcp_dl; >> > >> > > + uint16_t pyld_unit_size; >> > >> > > + uint16_t hdr_offset; >> > >> > > + int ret =3D 1; >> > >> > > + >> > >> > > + ipv4_hdr =3D (struct ipv4_hdr *)(rte_pktmbuf_mtod(pkt, char *= ) >> + >> > >> > > + pkt->l2_len); >> > >> > > + /* Don't process the fragmented packet */ >> > >> > > + if (unlikely((ipv4_hdr->fragment_offset & rte_cpu_to_be_16( >> > >> > > + >> IPV4_HDR_DF_MASK)) =3D=3D 0)) { >> > >> > >> > >> > >> > >> > It is not a check for fragmented packet - it is a check that >> fragmentation >> > >is allowed for that packet. >> > >> > Should be IPV4_HDR_DF_MASK - 1, I think. >> > > >> > >DF bit doesn't indicate is packet fragmented or not. >> > >It forbids to fragment packet any further. >> > >To check is packet already fragmented or not, you have to check MF bi= t >> and >> > >frag_offset. >> > >Both have to be zero for un-fragmented packets. >> > > >> > >> >> > >> IMO, IPV4_HDR_DF_MASK whose value is (1 << 14) is used to get DF bi= t. >> It's a >> > >> little-endian value. But ipv4_hdr->fragment_offset is big-endian or= der. >> > >> So the value of DF bit should be "ipv4_hdr->fragment_offset & >> > >rte_cpu_to_be_16( >> > >> IPV4_HDR_DF_MASK)". If this value is 0, the input packet is fragmen= ted. >> > >> >> > >> > >> > >> > > + pkts_out[0] =3D pkt; >> > >> > > + return ret; >> > >> > > + } >> > >> > > + >> > >> > > + tcp_dl =3D rte_be_to_cpu_16(ipv4_hdr->total_length) - pkt- >> >l3_len - >> > >> > > + pkt->l4_len; >> > >> > >> > >> > Why not use pkt->pkt_len - pkt->l2_len -pkt_l3_len - pkt_l4_len? >> > >> >> > >> Yes, we can use pkt->pkt_len - pkt->l2_len -pkt_l3_len - pkt_l4_len >here. >> > >> >> > >> > >> > >> > > + /* Don't process the packet without data */ >> > >> > > + if (unlikely(tcp_dl =3D=3D 0)) { >> > >> > > + pkts_out[0] =3D pkt; >> > >> > > + return ret; >> > >> > > + } >> > >> > > + >> > >> > > + hdr_offset =3D pkt->l2_len + pkt->l3_len + pkt->l4_len; >> > >> > > + pyld_unit_size =3D gso_size - hdr_offset - ETHER_CRC_LEN; >> > >> > >> > >> > Hmm, why do we need to count CRC_LEN here? >> > >> >> > >> Yes, we shouldn't count ETHER_CRC_LEN here. Its length should be >> > >> included in gso_size. >> > > >> > >Why? >> > >What is the point to account crc len into this computation? >> > >Why not just assume that gso_size is already a max_frame_size - crc_l= en >> > >As I remember, when we RX packet crc bytes will be already stripped, >> > >when user populates the packet, he doesn't care about crc bytes too. >> > >> > Hi Konstantin, >> > >> > When packet is tx'd, the 4B for CRC are added back into the packet; if= the >> payload is already at max capacity, then the actual segment size >> > will be 4B larger than expected (e.g. 1522B, as opposed to 1518B). >> > To prevent that from happening, we account for the CRC len in this >> calculation. >> >> >> Ok, and what prevents you to set gso_ctx.gso_size =3D 1514; /*ether fra= me >> size without crc bytes */ >> ? Hey Konstantin, If the user sets the gso_size to 1514, the resultant output segments' size = should be 1514, and not 1518. Consequently, the payload capacity of each se= gment would be reduced accordingly. The user only cares about the output segment size (i.e. gso_ctx.gso_size); = we need to ensure that the size of the segments that are produced is consis= tent with that. As a result, we need to ensure that any packet overhead is = accounted for in the segment size, before we can determine how much space r= emains for data. Hope this makes sense. Thanks, Mark =20 > >Exactly, applications can set 1514 to gso_segsz instead of 1518, if the lo= wer >layer >will add CRC to the packet. > >Jiayu > >> Konstantin >> >> > >> > If I've missed anything, please do let me know! >> > >> > Thanks, >> > Mark >> > >> > > >> > >Konstantin