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 09:00:36 +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> <2601191342CEEE43887BDE71AB9772584F24ADBC@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: "Ananyev, Konstantin" , "Hu, Jiayu" Return-path: Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by dpdk.org (Postfix) with ESMTP id 3574B199B4 for ; Thu, 14 Sep 2017 11:00:57 +0200 (CEST) In-Reply-To: <2601191342CEEE43887BDE71AB9772584F24ADBC@irsmsx105.ger.corp.intel.com> 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: Ananyev, Konstantin >Sent: Thursday, September 14, 2017 9:40 AM >To: Kavanagh, Mark B ; Hu, Jiayu > >Cc: dev@dpdk.org; Tan, Jianfeng >Subject: RE: [PATCH v3 2/5] gso: add TCP/IPv4 GSO support > > > >> -----Original Message----- >> From: Kavanagh, Mark B >> Sent: Thursday, September 14, 2017 9:35 AM >> To: Hu, Jiayu ; Ananyev, Konstantin > >> Cc: dev@dpdk.org; Tan, Jianfeng >> Subject: RE: [PATCH v3 2/5] gso: add TCP/IPv4 GSO support >> >> >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, cha= r *) >> >> + >> >> > >> > > + 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= bit >> >> 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 >bit. >> >> It's a >> >> > >> little-endian value. But ipv4_hdr->fragment_offset is big-endian >order. >> >> > >> 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 >fragmented. >> >> > >> >> >> > >> > >> >> > >> > > + 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_le= n? >> >> > >> >> >> > >> 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_len >> >> > >As I remember, when we RX packet crc bytes will be already strippe= d, >> >> > >when user populates the packet, he doesn't care about crc bytes to= o. >> >> > >> >> > 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 = frame >> >> size without crc bytes */ >> >> ? >> >> Hey Konstantin, >> >> If the user sets the gso_size to 1514, the resultant output segments' si= ze >should be 1514, and not 1518. Just to clarify - I meant here that the final output segment, including CRC= len, should be 1514. I think this is where we're crossing wires ;) > >Yes and then NIC HW will add CRC bytes for you. >You are not filling CRC bytes in HW, and when providing to the HW size to = send >- it is a payload size >(CRC bytes are not accounted). >Konstantin Yes, exactly - in that case though, the gso_size specified by the user is n= ot the actual final output segment size, but (segment size - 4B), right? We can set that expectation in documentation, but from an application's/use= r's perspective, do you think that this might be confusing/misleading? Thanks again, Mark =20 > > Consequently, the payload capacity >> of each segment 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 consistent with that. As a result, we need to ensure that an= y >packet overhead is accounted for in the segment size, before we >> can determine how much space remains for data. >> >> Hope this makes sense. >> >> Thanks, >> Mark >> >> > >> >Exactly, applications can set 1514 to gso_segsz instead of 1518, if the >lower >> >layer >> >will add CRC to the packet. >> > >> >Jiayu >> > >> >> Konstantin >> >> >> >> > >> >> > If I've missed anything, please do let me know! >> >> > >> >> > Thanks, >> >> > Mark >> >> > >> >> > > >> >> > >Konstantin