NAME

fi_tagged - Tagged data transfer operations

fi_trecv / fi_trecvv / fi_trecvmsg: Post a buffer to receive an incoming message
fi_tsend / fi_tsendv / fi_tsendmsg / fi_tinject / fi_tsenddata: Initiate an operation to send a message

SYNOPSIS

#include <rdma/fi_tagged.h>

ssize_t fi_trecv(struct fid_ep *ep, void *buf, size_t len, void *desc,
	fi_addr_t src_addr, uint64_t tag, uint64_t ignore, void *context);

ssize_t fi_trecvv(struct fid_ep *ep, const struct iovec *iov, void **desc,
	size_t count, fi_addr_t src_addr, uint64_t tag, uint64_t ignore,
	void *context);

ssize_t fi_trecvmsg(struct fid_ep *ep, const struct fi_msg_tagged *msg,
	uint64_t flags);

ssize_t fi_tsend(struct fid_ep *ep, const void *buf, size_t len,
	void *desc, fi_addr_t dest_addr, uint64_t tag, void *context);

ssize_t fi_tsendv(struct fid_ep *ep, const struct iovec *iov,
	void **desc, size_t count, fi_addr_t dest_addr, uint64_t tag,
	void *context);

ssize_t fi_tsendmsg(struct fid_ep *ep, const struct fi_msg_tagged *msg,
	uint64_t flags);

ssize_t fi_tinject(struct fid_ep *ep, const void *buf, size_t len,
	fi_addr_t dest_addr, uint64_t tag);

ssize_t fi_tsenddata(struct fid_ep *ep, const void *buf, size_t len,
	void *desc, uint64_t data, fi_addr_t dest_addr, uint64_t tag,
	void *context);

ssize_t fi_tinjectdata(struct fid_ep *ep, const void *buf, size_t len,
	uint64_t data, fi_addr_t dest_addr, uint64_t tag);

ARGUMENTS

fid: Fabric endpoint on which to initiate tagged communication operation.
buf: Data buffer to send or receive.
len: Length of data buffer to send or receive.
iov: Vectored data buffer.
count: Count of vectored data entries.
tag: Tag associated with the message.
ignore: Mask of bits to ignore applied to the tag for receive operations.
desc: Memory descriptor associated with the data buffer. See fi_mr(3).
data: Remote CQ data to transfer with the sent data.
dest_addr: Destination address for connectionless transfers. Ignored for connected endpoints.
src_addr: Source address to receive from for connectionless transfers. Applies only to connectionless endpoints with the FI_DIRECTED_RECV capability enabled, otherwise this field is ignored. If set to FI_ADDR_UNSPEC, any source address may match.
msg: Message descriptor for send and receive operations.
flags: Additional flags to apply for the send or receive operation.
context: User specified pointer to associate with the operation. This parameter is ignored if the operation will not generate a successful completion, unless an op flag specifies the context parameter be used for required input.

DESCRIPTION

Tagged messages are data transfers which carry a key or tag with the message buffer. The tag is used at the receiving endpoint to match the incoming message with a corresponding receive buffer. Message tags match when the receive buffer tag is the same as the send buffer tag with the ignored bits masked out. This can be stated as:

send_tag & ~ignore == recv_tag & ~ignore

In general, message tags are checked against receive buffers in the order in which messages have been posted to the endpoint. See the ordering discussion below for more details.

The send functions – fi_tsend, fi_tsendv, fi_tsendmsg, fi_tinject, and fi_tsenddata – are used to transmit a tagged message from one endpoint to another endpoint. The main difference between send functions are the number and type of parameters that they accept as input. Otherwise, they perform the same general function.

The receive functions – fi_trecv, fi_trecvv, fi_recvmsg – post a data buffer to an endpoint to receive inbound tagged messages. Similar to the send operations, receive operations operate asynchronously. Users should not touch the posted data buffer(s) until the receive operation has completed. Posted receive buffers are matched with inbound send messages based on the tags associated with the send and receive buffers.

An endpoint must be enabled before an application can post send or receive operations to it. For connected endpoints, receive buffers may be posted prior to connect or accept being called on the endpoint. This ensures that buffers are available to receive incoming data immediately after the connection has been established.

Completed message operations are reported to the user through one or more event collectors associated with the endpoint. Users provide context which are associated with each operation, and is returned to the user as part of the event completion. See fi_cq for completion event details.

fi_tsend

The call fi_tsend transfers the data contained in the user-specified data buffer to a remote endpoint, with message boundaries being maintained. The local endpoint must be connected to a remote endpoint or destination before fi_tsend is called. Unless the endpoint has been configured differently, the data buffer passed into fi_tsend must not be touched by the application until the fi_tsend call completes asynchronously.

fi_tsendv

The fi_tsendv call adds support for a scatter-gather list to fi_tsend. The fi_sendv transfers the set of data buffers referenced by the iov parameter to a remote endpoint as a single message.

fi_tsendmsg

The fi_tsendmsg call supports data transfers over both connected and connectionless endpoints, with the ability to control the send operation per call through the use of flags. The fi_tsendmsg function takes a struct fi_msg_tagged as input.

struct fi_msg_tagged {
	const struct iovec *msg_iov; /* scatter-gather array */
	void               *desc;    /* data descriptor */
	size_t             iov_count;/* # elements in msg_iov */
	fi_addr_t          addr;    /* optional endpoint address */
	uint64_t           tag;      /* tag associated with message */
	uint64_t           ignore;   /* mask applied to tag for receives */
	void               *context; /* user-defined context */
	uint64_t           data;     /* optional immediate data */
};

fi_tinject

The tagged inject call is an optimized version of fi_tsend. It provides similar completion semantics as fi_inject fi_msg(3).

fi_tsenddata

The tagged send data call is similar to fi_tsend, but allows for the sending of remote CQ data (see FI_REMOTE_CQ_DATA flag) as part of the transfer.

fi_tinjectdata

The tagged inject data call is similar to fi_tinject, but allows for the sending of remote CQ data (see FI_REMOTE_CQ_DATA flag) as part of the transfer.

fi_trecv

The fi_trecv call posts a data buffer to the receive queue of the corresponding endpoint. Posted receives are searched in the order in which they were posted in order to match sends. Message boundaries are maintained. The order in which the receives complete is dependent on the endpoint type and protocol.

fi_trecvv

The fi_trecvv call adds support for a scatter-gather list to fi_trecv. The fi_trecvv posts the set of data buffers referenced by the iov parameter to a receive incoming data.

fi_trecvmsg

The fi_trecvmsg call supports posting buffers over both connected and connectionless endpoints, with the ability to control the receive operation per call through the use of flags. The fi_trecvmsg function takes a struct fi_msg_tagged as input.

FLAGS

The fi_trecvmsg and fi_tsendmsg calls allow the user to specify flags which can change the default message handling of the endpoint. Flags specified with fi_trecvmsg / fi_tsendmsg override most flags previously configured with the endpoint, except where noted (see fi_endpoint). The following list of flags are usable with fi_trecvmsg and/or fi_tsendmsg.

FI_REMOTE_CQ_DATA: Applies to fi_tsendmsg and fi_tsenddata. Indicates that remote CQ data is available and should be sent as part of the request. See fi_getinfo for additional details on FI_REMOTE_CQ_DATA.
FI_COMPLETION: Indicates that a completion entry should be generated for the specified operation. The endpoint must be bound to a completion queue with FI_SELECTIVE_COMPLETION that corresponds to the specified operation, or this flag is ignored.
FI_MORE: Indicates that the user has additional requests that will immediately be posted after the current call returns. Use of this flag may improve performance by enabling the provider to optimize its access to the fabric hardware.
FI_INJECT: Applies to fi_tsendmsg. Indicates that the outbound data buffer should be returned to user immediately after the send call returns, even if the operation is handled asynchronously. This may require that the underlying provider implementation copy the data into a local buffer and transfer out of that buffer. This flag can only be used with messages smaller than inject_size.
FI_INJECT_COMPLETE: Applies to fi_tsendmsg. Indicates that a completion should be generated when the source buffer(s) may be reused.
FI_TRANSMIT_COMPLETE: Applies to fi_tsendmsg. Indicates that a completion should not be generated until the operation has been successfully transmitted and is no longer being tracked by the provider.
FI_MATCH_COMPLETE: Applies to fi_tsendmsg. Indicates that a completion should be generated only after the message has either been matched with a tagged buffer or was discarded by the target application.
FI_FENCE: Applies to transmits. Indicates that the requested operation, also known as the fenced operation, and any operation posted after the fenced operation will be deferred until all previous operations targeting the same peer endpoint have completed. Operations posted after the fencing will see and/or replace the results of any operations initiated prior to the fenced operation.
The ordering of operations starting at the posting of the fenced operation (inclusive) to the posting of a subsequent fenced operation (exclusive) is controlled by the endpoint’s ordering semantics.

The following flags may be used with fi_trecvmsg.

FI_PEEK

The peek flag may be used to see if a specified message has arrived. A peek request is often useful on endpoints that have provider allocated buffering enabled (see fi_rx_attr total_buffered_recv). Unlike standard receive operations, a receive operation with the FI_PEEK flag set does not remain queued with the provider after the peek completes successfully. The peek operation operates asynchronously, and the results of the peek operation are available in the completion queue associated with the endpoint. If no message is found matching the tags specified in the peek request, then a completion queue error entry with err field set to FI_ENOMSG will be available.

If a peek request locates a matching message, the operation will complete successfully. The returned completion data will indicate the meta-data associated with the message, such as the message length, completion flags, available CQ data, tag, and source address. The data available is subject to the completion entry format (e.g. struct fi_cq_tagged_entry).

An application may supply a buffer if it desires to receive data as a part of the peek operation. In order to receive data as a part of the peek operation, the buf and len fields must be available in the CQ format. In particular, FI_CQ_FORMAT_CONTEXT and FI_CQ_FORMAT_MSG cannot be used if peek operations desire to obtain a copy of the data. The returned data is limited to the size of the input buffer(s) or the message size, if smaller. A provider indicates if data is available by setting the buf field of the CQ entry to the user’s first input buffer. If buf is NULL, no data was available to return. A provider may return NULL even if the peek operation completes successfully. Note that the CQ entry len field will reference the size of the message, not necessarily the size of the returned data.

FI_CLAIM

If this flag is used in conjunction with FI_PEEK, it indicates if the peek request completes successfully – indicating that a matching message was located – the message is claimed by caller. Claimed messages can only be retrieved using a subsequent, paired receive operation with the FI_CLAIM flag set. A receive operation with the FI_CLAIM flag set, but FI_PEEK not set is used to retrieve a previously claimed message.

In order to use the FI_CLAIM flag, an application must supply a struct fi_context structure as the context for the receive operation, or a struct fi_recv_context in the case of buffered receives. The same fi_context structure used for an FI_PEEK + FI_CLAIM operation must be used by the paired FI_CLAIM request.

This flag also applies to endpoints configured for FI_BUFFERED_RECV or FI_VARIABLE_MSG. When set, it is used to retrieve a tagged message that was buffered by the provider. See Buffered Tagged Receives section for details.

FI_DISCARD

This flag may be used in conjunction with either FI_PEEK or FI_CLAIM. If this flag is used in conjunction with FI_PEEK, it indicates if the peek request completes successfully – indicating that a matching message was located – the message is discarded by the provider, as the data is not needed by the application. This flag may also be used in conjunction with FI_CLAIM in order to discard a message previously claimed using an FI_PEEK + FI_CLAIM request.

This flag also applies to endpoints configured for FI_BUFFERED_RECV or FI_VARIABLE_MSG. When set, it indicates that the provider should free a buffered messages. See Buffered Tagged Receives section for details.

If this flag is set, the input buffer(s) and length parameters are ignored.

Buffered Tagged Receives

See fi_msg(3) for an introduction to buffered receives. The handling of buffered receives differs between fi_msg operations and fi_tagged. Although the provider is responsible for allocating and managing network buffers, the application is responsible for identifying the tags that will be used to match incoming messages. The provider handles matching incoming receives to the application specified tags.

When FI_BUFFERED_RECV is enabled, the application posts the tags that will be used for matching purposes. Tags are posted using fi_trecv, fi_trecvv, and fi_trecvmsg; however, parameters related to the input buffers are ignored (e.g. buf, len, iov, desc). When a provider receives a message for which there is a matching tag, it will write an entry to the completion queue associated with the receiving endpoint.

For discussion purposes, the completion queue is assumed to be configured for FI_CQ_FORMAT_TAGGED. The op_context field will point to a struct fi_recv_context.

struct fi_recv_context {
	struct fid_ep *ep;
	void *context;
};

The ‘ep’ field will be NULL. The ‘context’ field will match the application context specified when posting the tag. Other fields are set as defined in fi_msg(3).

After being notified that a buffered receive has arrived, applications must either claim or discard the message as described in fi_msg(3).

Variable Length Tagged Messages

Variable length messages are defined in fi_msg(3). The requirements for handling variable length tagged messages is identical to those defined above for buffered tagged receives.

RETURN VALUE

The tagged send and receive calls return 0 on success. On error, a negative value corresponding to fabric _errno _ is returned. Fabric errno values are defined in fi_errno.h.

ERRORS

-FI_EAGAIN: See fi_msg(3) for a detailed description of handling FI_EAGAIN.
-FI_EINVAL: Indicates that an invalid argument was supplied by the user.
-FI_EOTHER: Indicates that an unspecified error occurred.

fi_tagged(3) Libfabric Programmer's Manual