91 lines · plain
1.. SPDX-License-Identifier: GPL-2.02 3=================================4Chelsio S3 iSCSI Driver for Linux5=================================6 7Introduction8============9 10The Chelsio T3 ASIC based Adapters (S310, S320, S302, S304, Mezz cards, etc.11series of products) support iSCSI acceleration and iSCSI Direct Data Placement12(DDP) where the hardware handles the expensive byte touching operations, such13as CRC computation and verification, and direct DMA to the final host memory14destination:15 16 - iSCSI PDU digest generation and verification17 18 On transmitting, Chelsio S3 h/w computes and inserts the Header and19 Data digest into the PDUs.20 On receiving, Chelsio S3 h/w computes and verifies the Header and21 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's26 payload into pre-posted final destination host-memory buffers based27 on the Initiator Task Tag (ITT) in Data-In or Target Task Tag (TTT)28 in Data-Out PDUs.29 30 - PDU Transmit and Recovery31 32 On transmitting, S3 h/w accepts the complete PDU (header + data)33 from the host driver, computes and inserts the digests, decomposes34 the PDU into multiple TCP segments if necessary, and transmit all35 the TCP segments onto the wire. It handles TCP retransmission if36 needed.37 38 On receiving, S3 h/w recovers the iSCSI PDU by reassembling TCP39 segments, separating the header and data, calculating and verifying40 the digests, then forwarding the header to the host. The payload data,41 if possible, will be directly placed into the pre-posted host DDP42 buffer. Otherwise, the payload data will be sent to the host too.43 44The cxgb3i driver interfaces with open-iscsi initiator and provides the iSCSI45acceleration through Chelsio hardware wherever applicable.46 47Using the cxgb3i Driver48=======================49 50The following steps need to be taken to accelerates the open-iscsi initiator:51 521. 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 Drivers59 SCSI device support --->60 [*] SCSI low-level drivers --->61 <M> Chelsio S3xx iSCSI support62 632. Create an interface file located under /etc/iscsi/ifaces/ for the new64 transport class "cxgb3i".65 66 The content of the file should be in the following format::67 68 iface.transport_name = cxgb3i69 iface.net_ifacename = <ethX>70 iface.ipaddress = <iscsi ip address>71 72 * if iface.ipaddress is specified, <iscsi ip address> needs to be either the73 same as the ethX's ip address or an address on the same subnet. Make74 sure the ip address is unique in the network.75 763. edit /etc/iscsi/iscsid.conf77 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 = 819281 82 * The login would fail for a normal session if MaxRecvDataSegmentLength is83 too big. A error message in the format of84 "cxgb3i: ERR! MaxRecvSegmentLength <X> too big. Need to be <= <Y>."85 would be logged to dmesg.86 874. 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 the89 iscsiadm command. <iface file name> is the transport interface file created90 in step 2.91