From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.droids-corp.org (zoll.droids-corp.org [94.23.50.67]) by dpdk.org (Postfix) with ESMTP id 467C27FD5 for ; Mon, 17 Nov 2014 12:11:31 +0100 (CET) Received: from was59-1-82-226-113-214.fbx.proxad.net ([82.226.113.214] helo=[192.168.0.10]) by mail.droids-corp.org with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:128) (Exim 4.80) (envelope-from ) id 1XqKQM-0000ne-9C; Mon, 17 Nov 2014 12:24:54 +0100 Message-ID: <5469DA40.7050107@6wind.com> Date: Mon, 17 Nov 2014 12:21:36 +0100 From: Olivier MATZ User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Icedove/24.5.0 MIME-Version: 1.0 To: "Liu, Jijiang" , Thomas Monjalon References: <1414376006-31402-1-git-send-email-jijiang.liu@intel.com> <176980123.CbUgamS8oi@xps13> <1ED644BD7E0A5F4091CF203DAFB8E4CC01D992F8@SHSMSX101.ccr.corp.intel.com> <3175184.TxKMqZeb6U@xps13> <1ED644BD7E0A5F4091CF203DAFB8E4CC01D9B646@SHSMSX101.ccr.corp.intel.com> <5465C6DD.4000000@6wind.com> <1ED644BD7E0A5F4091CF203DAFB8E4CC01D9BAC0@SHSMSX101.ccr.corp.intel.com> In-Reply-To: <1ED644BD7E0A5F4091CF203DAFB8E4CC01D9BAC0@SHSMSX101.ccr.corp.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: "dev@dpdk.org" Subject: Re: [dpdk-dev] [PATCH v8 10/10] app/testpmd:test VxLAN Tx checksum offload 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: Mon, 17 Nov 2014 11:11:31 -0000 Hi Jijiang, On 11/17/2014 07:52 AM, Liu, Jijiang wrote: > Anyway, I explain the checksum mechanism here again. > > In my VXLAN patch set, for an VXLAN packet TX checksum offload, the logics below: > > 1. only set outer L3/L4 header TX checksum > tx_checksum set 0x3(0r 0x1) 0 > In this case, the PKT_TX_VXLAN_CKSUM flag is not set as we don't set inner flags(PKT_TX_IPV4_CSUM, PKT_TX_UDP_CKSUM), so we don't need to change inner ones, driver think it is the ordinary packet, > HW will do outer L3/L4 checksum offload. Let's take an example with the following packet: Ether / IP / UDP / VxLAN / Ether / IP / UDP / data The original behavior (without your vxlan patches), which still works today, is to select inner or outer using the m->l2_len field: - checksum outer IP + UDP m->l2_len=14 m->l3_len=20 flags=PKT_TX_IP_CKSUM PKT_TX_UDP_CKSUM - checksum inner IP + UDP m->l2_len=64 m->l3_len=20 flags=PKT_TX_IP_CKSUM PKT_TX_UDP_CKSUM of course, the packet is valid only if the outer IP checksum is already correct and outer UDP checksum is 0 If i40e does not act like this, it does not follow the previous API. > 2. only set inner L3/L4 header TX checksum > tx_checksum set 0x30 0 > In this case, the PKT_TX_VXLAN_CKSUM flag is set, so driver think it is VXLAN packet, and we don't need to change outer ones because we don't set outer flags here (PKT_TX_IPV4_CSUM, PKT_TX_UDP_CKSUM). As explained above, there is no need to set the PKT_TX_VXLAN_CKSUM if you only want to set the inner L3/L4 checksum. This was already working like this before your patches, as long as l2_len and l3_len are set properly in the mbuf (l2_len should include the outer headers). Moreover, PKT_TX_IPV4_CSUM, PKT_TX_UDP_CKSUM, ... are not "outer flags". They are hardware checksum flags, and before your vxland patch, they concerned the headers referenced by m->l2_len and m->l3_len. With your vxlan patch, it changed without beeing documented. These flags use either (m->l2_len, m->l3_len) or (m->inner_l2_len, m->inner_l3_len), which is not a good idea in my opinion. > 3. set outer L3/L4 TX checksum and inner L3&L4 TX checksum > tx_checksum set 0x31(0x33) 0 > in this case, the PKT_TX_VXLAN_CKSUM flag is set, driver think it is VXLAN packet, and we need to change outer and inner as both outer and inner flags are set. Here you are talking about test pmd flags. You do not describe the mbuf API: PKT_TX_* flags and lengths values that need to be set (l2_len, l3_len, ...) and to what they refer to. I think if you want to explain the vxlan checksum offload mbuf API, you should not talk about the testpmd flags as: - they don't match the mbuf flags - they have undocumented (or uncoherent) behavior in the csumonly forward engine After several exchanges about this vxlan API. Unfortunately, it is still vague and obscure to me. So here is a proposition of API documentation that looks understandable. Maybe it is easier to change the code to match this API: PKT_TX_IP_CKSUM flag enables hardware computation of IP cksum. To use it: - fill l2_len and l3_len in mbuf - set the flag PKT_TX_IP_CKSUM - set the ip checksum to 0 in IP header See (1) and (2). One value among PKT_TX_L4_NO_CKSUM, PKT_TX_UDP_CKSUM, PKT_TX_TCP_CKSUM and PKT_TX_SCTP_CKSUM can be assigned to the bits of PKT_TX_L4_MASK. These flags are used to offload the L4 checksum in hardware. The user requires to: - fill l2_len and l3_len in mbuf - set the flags PKT_TX_TCP_CKSUM, PKT_TX_SCTP_CKSUM or PKT_TX_UDP_CKSUM - calculate the pseudo header checksum and set it in the L4 header (only for TCP or UDP). See rte_ipv4_phdr_cksum() and rte_ipv6_phdr_cksum(). For SCTP, set the crc field to 0. See (1) and (2). The PKT_TX_TCP_SEG flag can be set to enable TCP segmentation offload for a packet to be transmitted on hardware supporting TSO: - set the PKT_TX_TCP_SEG flag in mbuf->ol_flags (this flag implies PKT_TX_TCP_CKSUM) - if it's IPv4, set the PKT_TX_IP_CKSUM flag and write the IP checksum to 0 in the packet - fill the mbuf offload information: l2_len, l3_len, l4_len, tso_segsz - calculate the pseudo header checksum without taking ip_len in accound, and set it in the TCP header. Refer to rte_ipv4_phdr_cksum() and rte_ipv6_phdr_cksum() that can be used as helpers. See (1) and (2). (1) In case the packet is an encapsulated packet, the m->l2_len field can include all the outer tunnel headers. These headers will remain unmodified by the hardware. (2) If outer_l2_len and outer_l3_len are not 0, the beginning of the inner headers is relative to outer_l2_len + outer_l3_len. [To replace the PKT_TX_VXLAN_CKSUM, we introduce 2 new flags] PKT_TX_OUTER_IP_CKSUM flag enables hardware computation of IP cksum in outer headers. To use it: - fill outer_l2_len and outer_l3_len in mbuf - set the flag PKT_TX_OUTER_IP_CKSUM - set the ip checksum to 0 in outer IP header One value among PKT_TX_OUTER_L4_NO_CKSUM, PKT_TX_OUTER_UDP_CKSUM, PKT_TX_OUTER_TCP_CKSUM and PKT_TX_OUTER_SCTP_CKSUM can be assigned to the bits of PKT_TX_L4_MASK. These flags are used to offload the outer L4 checksum in hardware. The user requires to: - fill outer_l2_len and outer_l3_len in mbuf - set the flags PKT_TX_OUTER_TCP_CKSUM, PKT_TX_OUTER_SCTP_CKSUM or PKT_TX_OUTER_UDP_CKSUM - calculate the pseudo header checksum and set it in the outer L4 header (only for TCP or UDP). See rte_ipv4_phdr_cksum() and rte_ipv6_phdr_cksum(). For SCTP, set the crc field to 0. This proposition has several advantages: - it is documented :) - the API is straightforward: inner and outer work in the same manner. - the API already supports other tunnels (IPIP, GRE, STT, ...) - adding m->outer_* fields allows to keep the same semantic for the existing flags. Indeed, it does not map linux skb, but this is not an argument. Moreover, linux does not seem to support hardware tx checksum of outer+inner headers. Regards, Olivier