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Diffstat (limited to 'drivers/infiniband/ulp/rtrs/README')
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diff --git a/drivers/infiniband/ulp/rtrs/README b/drivers/infiniband/ulp/rtrs/README new file mode 100644 index 000000000..5d9ea142e --- /dev/null +++ b/drivers/infiniband/ulp/rtrs/README @@ -0,0 +1,213 @@ +**************************** +RDMA Transport (RTRS) +**************************** + +RTRS (RDMA Transport) is a reliable high speed transport library +which provides support to establish optimal number of connections +between client and server machines using RDMA (InfiniBand, RoCE, iWarp) +transport. It is optimized to transfer (read/write) IO blocks. + +In its core interface it follows the BIO semantics of providing the +possibility to either write data from an sg list to the remote side +or to request ("read") data transfer from the remote side into a given +sg list. + +RTRS provides I/O fail-over and load-balancing capabilities by using +multipath I/O (see "add_path" and "mp_policy" configuration entries in +Documentation/ABI/testing/sysfs-class-rtrs-client). + +RTRS is used by the RNBD (RDMA Network Block Device) modules. + +================== +Transport protocol +================== + +Overview +-------- +An established connection between a client and a server is called rtrs +session. A session is associated with a set of memory chunks reserved on the +server side for a given client for rdma transfer. A session +consists of multiple paths, each representing a separate physical link +between client and server. Those are used for load balancing and failover. +Each path consists of as many connections (QPs) as there are cpus on +the client. + +When processing an incoming write or read request, rtrs client uses memory +chunks reserved for him on the server side. Their number, size and addresses +need to be exchanged between client and server during the connection +establishment phase. Apart from the memory related information client needs to +inform the server about the session name and identify each path and connection +individually. + +On an established session client sends to server write or read messages. +Server uses immediate field to tell the client which request is being +acknowledged and for errno. Client uses immediate field to tell the server +which of the memory chunks has been accessed and at which offset the message +can be found. + +Module parameter always_invalidate is introduced for the security problem +discussed in LPC RDMA MC 2019. When always_invalidate=Y, on the server side we +invalidate each rdma buffer before we hand it over to RNBD server and +then pass it to the block layer. A new rkey is generated and registered for the +buffer after it returns back from the block layer and RNBD server. +The new rkey is sent back to the client along with the IO result. +The procedure is the default behaviour of the driver. This invalidation and +registration on each IO causes performance drop of up to 20%. A user of the +driver may choose to load the modules with this mechanism switched off +(always_invalidate=N), if he understands and can take the risk of a malicious +client being able to corrupt memory of a server it is connected to. This might +be a reasonable option in a scenario where all the clients and all the servers +are located within a secure datacenter. + + +Connection establishment +------------------------ + +1. Client starts establishing connections belonging to a path of a session one +by one via attaching RTRS_MSG_CON_REQ messages to the rdma_connect requests. +Those include uuid of the session and uuid of the path to be +established. They are used by the server to find a persisting session/path or +to create a new one when necessary. The message also contains the protocol +version and magic for compatibility, total number of connections per session +(as many as cpus on the client), the id of the current connection and +the reconnect counter, which is used to resolve the situations where +client is trying to reconnect a path, while server is still destroying the old +one. + +2. Server accepts the connection requests one by one and attaches +RTRS_MSG_CONN_RSP messages to the rdma_accept. Apart from magic and +protocol version, the messages include error code, queue depth supported by +the server (number of memory chunks which are going to be allocated for that +session) and the maximum size of one io, RTRS_MSG_NEW_RKEY_F flags is set +when always_invalidate=Y. + +3. After all connections of a path are established client sends to server the +RTRS_MSG_INFO_REQ message, containing the name of the session. This message +requests the address information from the server. + +4. Server replies to the session info request message with RTRS_MSG_INFO_RSP, +which contains the addresses and keys of the RDMA buffers allocated for that +session. + +5. Session becomes connected after all paths to be established are connected +(i.e. steps 1-4 finished for all paths requested for a session) + +6. Server and client exchange periodically heartbeat messages (empty rdma +messages with an immediate field) which are used to detect a crash on remote +side or network outage in an absence of IO. + +7. On any RDMA related error or in the case of a heartbeat timeout, the +corresponding path is disconnected, all the inflight IO are failed over to a +healthy path, if any, and the reconnect mechanism is triggered. + +CLT SRV +*for each connection belonging to a path and for each path: +RTRS_MSG_CON_REQ -------------------> + <------------------- RTRS_MSG_CON_RSP +... +*after all connections are established: +RTRS_MSG_INFO_REQ -------------------> + <------------------- RTRS_MSG_INFO_RSP +*heartbeat is started from both sides: + -------------------> [RTRS_HB_MSG_IMM] +[RTRS_HB_MSG_ACK] <------------------- +[RTRS_HB_MSG_IMM] <------------------- + -------------------> [RTRS_HB_MSG_ACK] + +IO path +------- + +* Write (always_invalidate=N) * + +1. When processing a write request client selects one of the memory chunks +on the server side and rdma writes there the user data, user header and the +RTRS_MSG_RDMA_WRITE message. Apart from the type (write), the message only +contains size of the user header. The client tells the server which chunk has +been accessed and at what offset the RTRS_MSG_RDMA_WRITE can be found by +using the IMM field. + +2. When confirming a write request server sends an "empty" rdma message with +an immediate field. The 32 bit field is used to specify the outstanding +inflight IO and for the error code. + +CLT SRV +usr_data + usr_hdr + rtrs_msg_rdma_write -----------------> [RTRS_IO_REQ_IMM] +[RTRS_IO_RSP_IMM] <----------------- (id + errno) + +* Write (always_invalidate=Y) * + +1. When processing a write request client selects one of the memory chunks +on the server side and rdma writes there the user data, user header and the +RTRS_MSG_RDMA_WRITE message. Apart from the type (write), the message only +contains size of the user header. The client tells the server which chunk has +been accessed and at what offset the RTRS_MSG_RDMA_WRITE can be found by +using the IMM field, Server invalidate rkey associated to the memory chunks +first, when it finishes, pass the IO to RNBD server module. + +2. When confirming a write request server sends an "empty" rdma message with +an immediate field. The 32 bit field is used to specify the outstanding +inflight IO and for the error code. The new rkey is sent back using +SEND_WITH_IMM WR, client When it recived new rkey message, it validates +the message and finished IO after update rkey for the rbuffer, then post +back the recv buffer for later use. + +CLT SRV +usr_data + usr_hdr + rtrs_msg_rdma_write -----------------> [RTRS_IO_REQ_IMM] +[RTRS_MSG_RKEY_RSP] <----------------- (RTRS_MSG_RKEY_RSP) +[RTRS_IO_RSP_IMM] <----------------- (id + errno) + + +* Read (always_invalidate=N)* + +1. When processing a read request client selects one of the memory chunks +on the server side and rdma writes there the user header and the +RTRS_MSG_RDMA_READ message. This message contains the type (read), size of +the user header, flags (specifying if memory invalidation is necessary) and the +list of addresses along with keys for the data to be read into. + +2. When confirming a read request server transfers the requested data first, +attaches an invalidation message if requested and finally an "empty" rdma +message with an immediate field. The 32 bit field is used to specify the +outstanding inflight IO and the error code. + +CLT SRV +usr_hdr + rtrs_msg_rdma_read --------------> [RTRS_IO_REQ_IMM] +[RTRS_IO_RSP_IMM] <-------------- usr_data + (id + errno) +or in case client requested invalidation: +[RTRS_IO_RSP_IMM_W_INV] <-------------- usr_data + (INV) + (id + errno) + +* Read (always_invalidate=Y)* + +1. When processing a read request client selects one of the memory chunks +on the server side and rdma writes there the user header and the +RTRS_MSG_RDMA_READ message. This message contains the type (read), size of +the user header, flags (specifying if memory invalidation is necessary) and the +list of addresses along with keys for the data to be read into. +Server invalidate rkey associated to the memory chunks first, when it finishes, +passes the IO to RNBD server module. + +2. When confirming a read request server transfers the requested data first, +attaches an invalidation message if requested and finally an "empty" rdma +message with an immediate field. The 32 bit field is used to specify the +outstanding inflight IO and the error code. The new rkey is sent back using +SEND_WITH_IMM WR, client When it recived new rkey message, it validates +the message and finished IO after update rkey for the rbuffer, then post +back the recv buffer for later use. + +CLT SRV +usr_hdr + rtrs_msg_rdma_read --------------> [RTRS_IO_REQ_IMM] +[RTRS_IO_RSP_IMM] <-------------- usr_data + (id + errno) +[RTRS_MSG_RKEY_RSP] <----------------- (RTRS_MSG_RKEY_RSP) +or in case client requested invalidation: +[RTRS_IO_RSP_IMM_W_INV] <-------------- usr_data + (INV) + (id + errno) +========================================= +Contributors List(in alphabetical order) +========================================= +Danil Kipnis <danil.kipnis@profitbricks.com> +Fabian Holler <mail@fholler.de> +Guoqing Jiang <guoqing.jiang@cloud.ionos.com> +Jack Wang <jinpu.wang@profitbricks.com> +Kleber Souza <kleber.souza@profitbricks.com> +Lutz Pogrell <lutz.pogrell@cloud.ionos.com> +Milind Dumbare <Milind.dumbare@gmail.com> +Roman Penyaev <roman.penyaev@profitbricks.com> |