1 .. SPDX-License-Identifier: GPL-2.0 2 3 ================================= 4 Chelsio S3 iSCSI Driver for Linux 5 ================================= 6 7 Introduction 8 ============ 9 10 The Chelsio T3 ASIC based Adapters (S310, S320, S302, S304, Mezz cards, etc. 11 series of products) support iSCSI acceleration and iSCSI Direct Data Placement 12 (DDP) where the hardware handles the expensive byte touching operations, such 13 as CRC computation and verification, and direct DMA to the final host memory 14 destination: 15 16 - iSCSI PDU digest generation and verification 17 18 On transmitting, Chelsio S3 h/w computes and inserts the Header and 19 Data digest into the PDUs. 20 On receiving, Chelsio S3 h/w computes and verifies the Header and 21 Data digest of the PDUs. 22 23 - Direct Data Placement (DDP) 24 25 S3 h/w can directly place the iSCSI Data-In or Data-Out PDU's 26 payload into pre-posted final destination host-memory buffers based 27 on the Initiator Task Tag (ITT) in Data-In or Target Task Tag (TTT) 28 in Data-Out PDUs. 29 30 - PDU Transmit and Recovery 31 32 On transmitting, S3 h/w accepts the complete PDU (header + data) 33 from the host driver, computes and inserts the digests, decomposes 34 the PDU into multiple TCP segments if necessary, and transmit all 35 the TCP segments onto the wire. It handles TCP retransmission if 36 needed. 37 38 On receiving, S3 h/w recovers the iSCSI PDU by reassembling TCP 39 segments, separating the header and data, calculating and verifying 40 the digests, then forwarding the header to the host. The payload data, 41 if possible, will be directly placed into the pre-posted host DDP 42 buffer. Otherwise, the payload data will be sent to the host too. 43 44 The cxgb3i driver interfaces with open-iscsi initiator and provides the iSCSI 45 acceleration through Chelsio hardware wherever applicable. 46 47 Using the cxgb3i Driver 48 ======================= 49 50 The following steps need to be taken to accelerates the open-iscsi initiator: 51 52 1. Load the cxgb3i driver: "modprobe cxgb3i" 53 54 The cxgb3i module registers a new transport class "cxgb3i" with open-iscsi. 55 56 * in the case of recompiling the kernel, the cxgb3i selection is located at:: 57 58 Device Drivers 59 SCSI device support ---> 60 [*] SCSI low-level drivers ---> 61 <M> Chelsio S3xx iSCSI support 62 63 2. Create an interface file located under /etc/iscsi/ifaces/ for the new 64 transport class "cxgb3i". 65 66 The content of the file should be in the following format:: 67 68 iface.transport_name = cxgb3i 69 iface.net_ifacename = <ethX> 70 iface.ipaddress = <iscsi ip address> 71 72 * if iface.ipaddress is specified, <iscsi ip address> needs to be either the 73 same as the ethX's ip address or an address on the same subnet. Make 74 sure the ip address is unique in the network. 75 76 3. edit /etc/iscsi/iscsid.conf 77 The default setting for MaxRecvDataSegmentLength (131072) is too big; 78 replace with a value no bigger than 15360 (for example 8192):: 79 80 node.conn[0].iscsi.MaxRecvDataSegmentLength = 8192 81 82 * The login would fail for a normal session if MaxRecvDataSegmentLength is 83 too big. A error message in the format of 84 "cxgb3i: ERR! MaxRecvSegmentLength <X> too big. Need to be <= <Y>." 85 would be logged to dmesg. 86 87 4. To direct open-iscsi traffic to go through cxgb3i's accelerated path, 88 "-I <iface file name>" option needs to be specified with most of the 89 iscsiadm command. <iface file name> is the transport interface file created 90 in step 2.
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