fi_endpoint man page

fi_endpoint — Fabric endpoint operations

fi_endpoint / fi_scalable_ep / fi_passive_ep / fi_close
Allocate or close an endpoint.
fi_ep_bind
Associate an endpoint with an event queue, completion queue, counter, or address vector
fi_scalable_ep_bind
Associate a scalable endpoint with an address vector
fi_pep_bind
Associate a passive endpoint with an event queue
fi_enable
Transitions an active endpoint into an enabled state.
fi_cancel
Cancel a pending asynchronous data transfer
fi_ep_alias
Create an alias to the endpoint
fi_control
Control endpoint operation.
fi_getopt / fi_setopt
Get or set endpoint options.
fi_rx_context / fi_tx_context / fi_srx_context / fi_stx_context
Open a transmit or receive context.
fi_rx_size_left / fi_tx_size_left
Query the lower bound on how many RX/TX operations may be posted without an operation returning -FI_EAGAIN.

Synopsis

#include <rdma/fabric.h>

#include <rdma/fi_endpoint.h>

int fi_endpoint(struct fid_domain *domain, struct fi_info *info,
    struct fid_ep **ep, void *context);

int fi_scalable_ep(struct fid_domain *domain, struct fi_info *info,
    struct fid_ep **sep, void *context);

int fi_passive_ep(struct fi_fabric *fabric, struct fi_info *info,
    struct fid_pep **pep, void *context);

int fi_tx_context(struct fid_ep *sep, int index,
    struct fi_tx_attr *attr, struct fid_ep **tx_ep,
    void *context);

int fi_rx_context(struct fid_ep *sep, int index,
    struct fi_rx_attr *attr, struct fid_ep **rx_ep,
    void *context);

int fi_stx_context(struct fid_domain *domain,
    struct fi_tx_attr *attr, struct fid_stx **stx,
    void *context);

int fi_srx_context(struct fid_domain *domain,
    struct fi_rx_attr *attr, struct fid_ep **rx_ep,
    void *context);

int fi_close(struct fid *ep);

int fi_ep_bind(struct fid_ep *ep, struct fid *fid, uint64_t flags);

int fi_scalable_ep_bind(struct fid_ep *sep, struct fid *fid, uint64_t flags);

int fi_pep_bind(struct fid_pep *pep, struct fid *fid, uint64_t flags);

int fi_enable(struct fid_ep *ep);

int fi_cancel(struct fid_ep *ep, void *context);

int fi_ep_alias(struct fid_ep *ep, struct fid_ep **alias_ep, uint64_t flags);

int fi_control(struct fid *ep, int command, void *arg);

int fi_getopt(struct fid *ep, int level, int optname,
    void *optval, size_t *optlen);

int fi_setopt(struct fid *ep, int level, int optname,
    const void *optval, size_t optlen);

ssize_t fi_rx_size_left(struct fid_ep *ep);

ssize_t fi_tx_size_left(struct fid_ep *ep);

Arguments

fid : On creation, specifies a fabric or access domain. On bind, identifies the event queue, completion queue, counter, or address vector to bind to the endpoint. In other cases, it's a fabric identifier of an associated resource.

info : Details about the fabric interface endpoint to be opened, obtained from fi_getinfo.

ep : A fabric endpoint.

sep : A scalable fabric endpoint.

pep : A passive fabric endpoint.

context : Context associated with the endpoint or asynchronous operation.

index : Index to retrieve a specific transmit/receive context.

attr : Transmit or receive context attributes.

flags : Additional flags to apply to the operation.

command : Command of control operation to perform on endpoint.

arg : Optional control argument.

level : Protocol level at which the desired option resides.

optname : The protocol option to read or set.

optval : The option value that was read or to set.

optlen : The size of the optval buffer.

Description

Endpoints are transport level communication portals. There are two types of endpoints: active and passive. Passive endpoints belong to a fabric domain and are most often used to listen for incoming connection requests. However, a passive endpoint may be used to reserve a fabric address that can be granted to an active endpoint. Active endpoints belong to access domains and can perform data transfers.

Active endpoints may be connection-oriented or connectionless, and may provide data reliability. The data transfer interfaces -- messages (fi_msg), tagged messages (fi_tagged), RMA (fi_rma), and atomics (fi_atomic) -- are associated with active endpoints. In basic configurations, an active endpoint has transmit and receive queues. In general, operations that generate traffic on the fabric are posted to the transmit queue. This includes all RMA and atomic operations, along with sent messages and sent tagged messages. Operations that post buffers for receiving incoming data are submitted to the receive queue.

Active endpoints are created in the disabled state. They must transition into an enabled state before accepting data transfer operations, including posting of receive buffers. The fi_enable call is used to transition an active endpoint into an enabled state. The fi_connect and fi_accept calls will also transition an endpoint into the enabled state, if it is not already active.

In order to transition an endpoint into an enabled state, it must be bound to one or more fabric resources. An endpoint that will generate asynchronous completions, either through data transfer operations or communication establishment events, must be bound to the appropriate completion queues or event queues, respectively, before being enabled. Unconnected endpoints must be bound to an address vector.

Once an endpoint has been activated, it may be associated with an address vector. Receive buffers may be posted to it and calls may be made to connection establishment routines. Connectionless endpoints may also perform data transfers.

The behavior of an endpoint may be adjusted by setting its control data and protocol options. This allows the underlying provider to redirect function calls to implementations optimized to meet the desired application behavior.

If an endpoint experiences a critical error, it will transition back into a disabled state. Critical errors are reported through the event queue associated with the EP. In certain cases, a disabled endpoint may be re-enabled. The ability to transition back into an enabled state is provider specific and depends on the type of error that the endpoint experienced. When an endpoint is disabled as a result of a critical error, all pending operations are discarded.

fi_endpoint / fi_passive_ep / fi_scalable_ep

fi_endpoint allocates a new active endpoint. fi_passive_ep allocates a new passive endpoint. fi_scalable_ep allocates a scalable endpoint. The properties and behavior of the endpoint are defined based on the provided struct fi_info. See fi_getinfo for additional details on fi_info. fi_info flags that control the operation of an endpoint are defined below. See section Scalable Endpoints.

If an active endpoint is allocated in order to accept a connection request, the fi_info parameter must be the same as the fi_info structure provided with the connection request (FI_CONNREQ) event.

An active endpoint may acquire the properties of a passive endpoint by setting the fi_info handle field to the passive endpoint fabric descriptor. This is useful for applications that need to reserve the fabric address of an endpoint prior to knowing if the endpoint will be used on the active or passive side of a connection. For example, this feature is useful for simulating socket semantics. Once an active endpoint acquires the properties of a passive endpoint, the passive endpoint is no longer bound to any fabric resources and must no longer be used. The user is expected to close the passive endpoint after opening the active endpoint in order to free up any lingering resources that had been used.

fi_close

Closes an endpoint and release all resources associated with it.

When closing a scalable endpoint, there must be no opened transmit contexts, or receive contexts associated with the scalable endpoint. If resources are still associated with the scalable endpoint when attempting to close, the call will return -FI_EBUSY.

Outstanding operations posted to the endpoint when fi_close is called will be discarded. Discarded operations will silently be dropped, with no completions reported. Additionally, a provider may discard previously completed operations from the associated completion queue(s). The behavior to discard completed operations is provider specific.

fi_ep_bind

fi_ep_bind is used to associate an endpoint with hardware resources. The common use of fi_ep_bind is to direct asynchronous operations associated with an endpoint to a completion queue. An endpoint must be bound with CQs capable of reporting completions for any asynchronous operation initiated on the endpoint. This is true even for endpoints which are configured to suppress successful completions, in order that operations that complete in error may be reported to the user. For passive endpoints, this requires binding the endpoint with an EQ that supports the communication management (CM) domain.

An active endpoint may direct asynchronous completions to different CQs, based on the type of operation. This is specified using fi_ep_bind flags. The following flags may be used separately or OR'ed together when binding an endpoint to a completion domain CQ.

FI_TRANSMIT : Directs the completion of outbound data transfer requests to the specified completion queue. This includes send message, RMA, and atomic operations.

FI_RECV : Directs the notification of inbound data transfers to the specified completion queue. This includes received messages. This binding automatically includes FI_REMOTE_WRITE, if applicable to the endpoint.

FI_SELECTIVE_COMPLETION : By default, data transfer operations generate completion entries into a completion queue after they have successfully completed. Applications can use this bind flag to selectively enable when completions are generated. If FI_SELECTIVE_COMPLETION is specified, data transfer operations will not generate entries for successful completions unless FI_COMPLETION is set as an operational flag for the given operation. FI_SELECTIVE_COMPLETION must be OR'ed with FI_TRANSMIT and/or FI_RECV flags.

When FI_SELECTIVE_COMPLETION is set, the user must determine when a request that does NOT have FI_COMPLETION set has completed indirectly, usually based on the completion of a subsequent operation. Use of this flag may improve performance by allowing the provider to avoid writing a completion entry for every operation.

Example: An application can selectively generate send completions by using the following general approach:

fi_tx_attr::op_flags = 0; // default - no completion
fi_ep_bind(ep, cq, FI_TRANSMIT | FI_SELECTIVE_COMPLETION);
fi_send(ep, ...);                   // no completion
fi_sendv(ep, ...);                  // no completion
fi_sendmsg(ep, ..., FI_COMPLETION); // completion!
fi_inject(ep, ...);                 // no completion

Example: An application can selectively disable send completions by modifying the operational flags:

fi_tx_attr::op_flags = FI_COMPLETION; // default - completion
fi_ep_bind(ep, cq, FI_TRANSMIT | FI_SELECTIVE_COMPLETION);
fi_send(ep, ...);       // completion
fi_sendv(ep, ...);      // completion
fi_sendmsg(ep, ..., 0); // no completion!
fi_inject(ep, ...);     // no completion!

Example: Omitting FI_SELECTIVE_COMPLETION when binding will generate completions for all non-fi_inject calls:

fi_tx_attr::op_flags = 0;
fi_ep_bind(ep, cq, FI_TRANSMIT);    // default - completion
fi_send(ep, ...);                   // completion
fi_sendv(ep, ...);                  // completion
fi_sendmsg(ep, ..., 0);             // completion!
fi_sendmsg(ep, ..., FI_COMPLETION); // completion
fi_sendmsg(ep, ..., FI_INJECT|FI_COMPLETION); // completion!
fi_inject(ep, ...);                 // no completion!

An endpoint may also, or instead, be bound to a fabric counter. When binding an endpoint to a counter, the following flags may be specified.

FI_SEND : Increments the specified counter whenever a message transfer initiated over the endpoint has completed successfully or in error. Sent messages include both tagged and normal message operations.

FI_RECV : Increments the specified counter whenever a message is received over the endpoint. Received messages include both tagged and normal message operations.

FI_READ : Increments the specified counter whenever an RMA read or atomic fetch operation initiated from the endpoint has completed successfully or in error.

FI_WRITE : Increments the specified counter whenever an RMA write or atomic operation initiated from the endpoint has completed successfully or in error.

FI_REMOTE_READ : Increments the specified counter whenever an RMA read or atomic fetch operation is initiated from a remote endpoint that targets the given endpoint. Use of this flag requires that the endpoint be created using FI_RMA_EVENT.

FI_REMOTE_WRITE : Increments the specified counter whenever an RMA write or atomic operation is initiated from a remote endpoint that targets the given endpoint. Use of this flag requires that the endpoint be created using FI_RMA_EVENT.

Connectionless endpoints must be bound to a single address vector. If an endpoint is using a shared transmit and/or receive context, the shared contexts must be bound to the endpoint. CQs, counters, AV, and shared contexts must be bound to endpoints before they are enabled.

fi_scalable_ep_bind

fi_scalable_ep_bind is used to associate a scalable endpoint with an address vector. See section on Scalable Endpoints. A scalable endpoint has a single transport level address and can support multiple transmit and receive contexts. The transmit and receive contexts share the transport-level address. Address vectors that are bound to scalable endpoints are implicitly bound to any transmit or receive contexts created using the scalable endpoint.

fi_enable

This call transitions the endpoint into an enabled state. An endpoint must be enabled before it may be used to perform data transfers. Enabling an endpoint typically results in hardware resources being assigned to it. Endpoints making use of completion queues, counters, event queues, and/or address vectors must be bound to them before being enabled.

Calling connect or accept on an endpoint will implicitly enable an endpoint if it has not already been enabled.

fi_enable may also be used to re-enable an endpoint that has been disabled as a result of experiencing a critical error. Applications should check the return value from fi_enable to see if a disabled endpoint has successfully be re-enabled.

fi_cancel

fi_cancel attempts to cancel an outstanding asynchronous operation. Canceling an operation causes the fabric provider to search for the operation and, if it is still pending, complete it as having been canceled. An error queue entry will be available in the the associated error queue with error code FI_ECANCELED. On the other hand, if the operation completed before the call to fi_cancel, then the completion status of that operation will be available in the associated completion queue. No specific entry related to fi_cancel itself will be posted. If multiple outstanding operations match the context parameter, only one will be canceled. In this case, the operation which is canceled is provider specific. The cancel operation is asynchronous, but will complete within a bounded period of time.

fi_ep_alias

This call creates an alias to the specified endpoint. Conceptually, an endpoint alias provides an alternate software path from the application to the underlying provider hardware. Applications configure an alias endpoint with data transfer flags, specified through the fi_ep_alias call. The flags must include FI_TRANSMIT or FI_RECV (not both) with other flags OR'ed to indicate the type of data transfer the flags should apply to. This will override the transmit and receive attributes of the alias endpoint. Typically the attributes of the alias endpoint are different than those assigned to the actual endpoint. The alias mechanism allows a single endpoint to have multiple optimized software interfaces. All allocated aliases must be closed for the underlying endpoint to be released.

fi_control

The control operation is used to adjust the default behavior of an endpoint. It allows the underlying provider to redirect function calls to implementations optimized to meet the desired application behavior. As a result, calls to fi_ep_control must be serialized against all other calls to an endpoint.

The base operation of an endpoint is selected during creation using struct fi_info. The following control commands and arguments may be assigned to an endpoint.

**FI_GETOPSFLAG -- uint64_t *flags** : Used to retrieve the current value of flags associated with the data transfer operations initiated on the endpoint. The control argument must include FI_TRANSMIT or FI_RECV (not both) flags to indicate the type of data transfer flags to be returned. See below for a list of control flags.

**FI_SETOPSFLAG -- uint64_t *flags** : Used to change the data transfer operation flags associated with an endpoint. The control argument must include FI_TRANSMIT or FI_RECV (not both) to indicate the type of data transfer that the flags should apply to, with other flags OR'ed in. The given flags will override the previous transmit and receive attributes that were set when the endpoint was created. Valid control flags are defined below.

**FI_BACKLOG - int *value** : This option only applies to passive endpoints. It is used to set the connection request backlog for listening endpoints.

fi_getopt / fi_setopt

Endpoint protocol operations may be retrieved using fi_getopt or set using fi_setopt. Applications specify the level that a desired option exists, identify the option, and provide input/output buffers to get or set the option. fi_setopt provides an application a way to adjust low-level protocol and implementation specific details of an endpoint.

The following option levels and option names and parameters are defined.

FI_OPT_ENDPOINT

·
FI_OPT_MIN_MULTI_RECV - size_t : Defines the minimum receive buffer space available when the receive buffer is automatically freed (see FI_MULTI_RECV). Modifying this value is only guaranteed to set the minimum buffer space needed on receives posted after the value has been changed. It is recommended that applications that want to override the default MIN_MULTI_RECV value set this option before enabling the corresponding endpoint.
·
FI_OPT_CM_DATA_SIZE - size_t : Defines the size of available space in CM messages for user-defined data. This value limits the amount of data that applications can exchange between peer endpoints using the fi_connect, fi_accept, and fi_reject operations. The size returned is dependent upon the properties of the endpoint, except in the case of passive endpoints, in which the size reflects the maximum size of the data that may be present as part of a connection request event. This option is read only.

fi_rx_size_left

The fi_rx_size_left call returns a lower bound on the number of receive operations that may be posted to the given endpoint without that operation returning -FI_EAGAIN. Depending on the specific details of the subsequently posted receive operations (e.g., number of iov entries, which receive function is called, etc.), it may be possible to post more receive operations than originally indicated by fi_rx_size_left.

fi_tx_size_left

The fi_tx_size_left call returns a lower bound on the number of transmit operations that may be posted to the given endpoint without that operation returning -FI_EAGAIN. Depending on the specific details of the subsequently posted transmit operations (e.g., number of iov entries, which transmit function is called, etc.), it may be possible to post more transmit operations than originally indicated by fi_tx_size_left.

Endpoint Attributes

The fi_ep_attr structure defines the set of attributes associated with an endpoint. Endpoint attributes may be further refined using the transmit and receive context attributes as shown below.

struct fi_ep_attr {
    enum fi_ep_type type;
    uint32_t        protocol;
    uint32_t        protocol_version;
    size_t          max_msg_size;
    size_t          msg_prefix_size;
    size_t          max_order_raw_size;
    size_t          max_order_war_size;
    size_t          max_order_waw_size;
    uint64_t        mem_tag_format;
    size_t          tx_ctx_cnt;
    size_t          rx_ctx_cnt;
};

type - Endpoint Type

If specified, indicates the type of fabric interface communication desired. Supported types are:

FI_EP_UNSPEC : The type of endpoint is not specified. This is usually provided as input, with other attributes of the endpoint or the provider selecting the type.

FI_EP_MSG : Provides a reliable, connection-oriented data transfer service with flow control that maintains message boundaries.

FI_EP_DGRAM : Supports a connectionless, unreliable datagram communication. Message boundaries are maintained, but the maximum message size may be limited to the fabric MTU. Flow control is not guaranteed.

FI_EP_RDM : Reliable datagram message. Provides a reliable, unconnected data transfer service with flow control that maintains message boundaries.

Protocol

Specifies the low-level end to end protocol employed by the provider. A matching protocol must be used by communicating endpoints to ensure interoperability. The following protocol values are defined. Provider specific protocols are also allowed. Provider specific protocols will be indicated by having the upper bit of the protocol value set to one.

FI_PROTO_UNSPEC : The protocol is not specified. This is usually provided as input, with other attributes of the socket or the provider selecting the actual protocol.

FI_PROTO_RDMA_CM_IB_RC : The protocol runs over Infiniband reliable-connected queue pairs, using the RDMA CM protocol for connection establishment.

FI_PROTO_IWARP : The protocol runs over the Internet wide area RDMA protocol transport.

FI_PROTO_IB_UD : The protocol runs over Infiniband unreliable datagram queue pairs.

FI_PROTO_PSMX : The protocol is based on an Intel proprietary protocol known as PSM, performance scaled messaging. PSMX is an extended version of the PSM protocol to support the libfabric interfaces.

FI_PROTO_UDP : The protocol sends and receives UDP datagrams. For example, an endpoint using FI_PROTO_UDP will be able to communicate with a remote peer that is using Berkeley SOCK_DGRAM sockets using IPPROTO_UDP.

FI_PROTO_SOCK_TCP : The protocol is layered over TCP packets.

protocol_version - Protocol Version

Identifies which version of the protocol is employed by the provider. The protocol version allows providers to extend an existing protocol, by adding support for additional features or functionality for example, in a backward compatible manner. Providers that support different versions of the same protocol should inter-operate, but only when using the capabilities defined for the lesser version.

max_msg_size - Max Message Size

Defines the maximum size for an application data transfer as a single operation.

msg_prefix_size - Message Prefix Size

Specifies the size of any required message prefix buffer space. This field will be 0 unless the FI_MSG_PREFIX mode is enabled. If msg_prefix_size is > 0 the specified value will be a multiple of 8-bytes.

Max RMA Ordered Size

The maximum ordered size specifies the delivery order of transport data into target memory for RMA and atomic operations. Data ordering is separate, but dependent on message ordering (defined below). Data ordering is unspecified where message order is not defined.

Data ordering refers to the access of target memory by subsequent operations. When back to back RMA read or write operations access the same registered memory location, data ordering indicates whether the second operation reads or writes the target memory after the first operation has completed. Because RMA ordering applies between two operations, and not within a single data transfer, ordering is defined per byte-addressable memory location. I.e. ordering specifies whether location X is accessed by the second operation after the first operation. Nothing is implied about the completion of the first operation before the second operation is initiated.

In order to support large data transfers being broken into multiple packets and sent using multiple paths through the fabric, data ordering may be limited to transfers of a specific size or less. Providers specify when data ordering is maintained through the following values. Note that even if data ordering is not maintained, message ordering may be.

max_order_raw_size : Read after write size. If set, an RMA or atomic read operation issued after an RMA or atomic write operation, both of which are smaller than the size, will be ordered. Where the target memory locations overlap, the RMA or atomic read operation will see the results of the previous RMA or atomic write.

max_order_war_size : Write after read size. If set, an RMA or atomic write operation issued after an RMA or atomic read operation, both of which are smaller than the size, will be ordered. The RMA or atomic read operation will see the initial value of the target memory location before a subsequent RMA or atomic write updates the value.

max_order_waw_size : Write after write size. If set, an RMA or atomic write operation issued after an RMA or atomic write operation, both of which are smaller than the size, will be ordered. The target memory location will reflect the results of the second RMA or atomic write.

An order size value of 0 indicates that ordering is not guaranteed. A value of -1 guarantees ordering for any data size.

mem_tag_format - Memory Tag Format

The memory tag format is a bit array used to convey the number of tagged bits supported by a provider. Additionally, it may be used to divide the bit array into separate fields. The mem_tag_format optionally begins with a series of bits set to 0, to signify bits which are ignored by the provider. Following the initial prefix of ignored bits, the array will consist of alternating groups of bits set to all 1's or all 0's. Each group of bits corresponds to a tagged field. The implication of defining a tagged field is that when a mask is applied to the tagged bit array, all bits belonging to a single field will either be set to 1 or 0, collectively.

For example, a mem_tag_format of 0x30FF indicates support for 14 tagged bits, separated into 3 fields. The first field consists of 2-bits, the second field 4-bits, and the final field 8-bits. Valid masks for such a tagged field would be a bitwise OR'ing of zero or more of the following values: 0x3000, 0x0F00, and 0x00FF.

By identifying fields within a tag, a provider may be able to optimize their search routines. An application which requests tag fields must provide tag masks that either set all mask bits corresponding to a field to all 0 or all 1. When negotiating tag fields, an application can request a specific number of fields of a given size. A provider must return a tag format that supports the requested number of fields, with each field being at least the size requested, or fail the request. A provider may increase the size of the fields. When reporting completions (see FI_CQ_FORMAT_TAGGED), the provider must provide the exact value of the received tag, clearing out any unsupported tag bits.

It is recommended that field sizes be ordered from smallest to largest. A generic, unstructured tag and mask can be achieved by requesting a bit array consisting of alternating 1's and 0's.

tx_ctx_cnt - Transmit Context Count

Number of transmit contexts to associate with the endpoint. If not specified (0), 1 context will be assigned if the endpoint supports outbound transfers. Transmit contexts are independent transmit queues that may be separately configured. Each transmit context may be bound to a separate CQ, and no ordering is defined between contexts. Additionally, no synchronization is needed when accessing contexts in parallel.

If the count is set to the value FI_SHARED_CONTEXT, the endpoint will be configured to use a shared transmit context, if supported by the provider. Providers that do not support shared transmit contexts will fail the request.

See the scalable endpoint and shared contexts sections for additional details.

rx_ctx_cnt - Receive Context Count

Number of receive contexts to associate with the endpoint. If not specified, 1 context will be assigned if the endpoint supports inbound transfers. Receive contexts are independent processing queues that may be separately configured. Each receive context may be bound to a separate CQ, and no ordering is defined between contexts. Additionally, no synchronization is needed when accessing contexts in parallel.

If the count is set to the value FI_SHARED_CONTEXT, the endpoint will be configured to use a shared receive context, if supported by the provider. Providers that do not support shared receive contexts will fail the request.

See the scalable endpoint and shared contexts sections for additional details.

Transmit Context Attributes

Attributes specific to the transmit capabilities of an endpoint are specified using struct fi_tx_attr.

struct fi_tx_attr {
    uint64_t  caps;
    uint64_t  mode;
    uint64_t  op_flags;
    uint64_t  msg_order;
    uint64_t  comp_order;
    size_t    inject_size;
    size_t    size;
    size_t    iov_limit;
    size_t    rma_iov_limit;
};

caps - Capabilities

The requested capabilities of the context. The capabilities must be a subset of those requested of the associated endpoint. See the CAPABILITIES section of fi_getinfo(3) for capability details. If the caps field is 0 on input to fi_getinfo(3), the caps value from the fi_info structure will be used.

mode

The operational mode bits of the context. The mode bits will be a subset of those associated with the endpoint. See the Mode section of fi_getinfo(3) for details. A mode value of 0 will be ignored on input to fi_getinfo(3), with the mode value of the fi_info structure used instead. On return from fi_getinfo(3), the mode will be set only to those constraints specific to transmit operations.

op_flags - Default transmit operation flags

Flags that control the operation of operations submitted against the context. Applicable flags are listed in the Operation Flags section.

msg_order - Message Ordering

Message ordering refers to the order in which transport layer headers (as viewed by the application) are processed. Relaxed message order enables data transfers to be sent and received out of order, which may improve performance by utilizing multiple paths through the fabric from the initiating endpoint to a target endpoint. Message order applies only between a single source and destination endpoint pair. Ordering between different target endpoints is not defined.

Message order is determined using a set of ordering bits. Each set bit indicates that ordering is maintained between data transfers of the specified type. Message order is defined for [read | write | send] operations submitted by an application after [read | write | send] operations.

Message ordering only applies to the end to end transmission of transport headers. Message ordering is necessary, but does not guarantee, the order in which message data is sent or received by the transport layer. Message ordering requires matching ordering semantics on the receiving side of a data transfer operation in order to guarantee that ordering is met.

FI_ORDER_NONE : No ordering is specified. This value may be used as input in order to obtain the default message order supported by the provider. FI_ORDER_NONE is an alias for the value 0.

FI_ORDER_RAR : Read after read. If set, RMA and atomic read operations are transmitted in the order submitted relative to other RMA and atomic read operations. If not set, RMA and atomic reads may be transmitted out of order from their submission.

FI_ORDER_RAW : Read after write. If set, RMA and atomic read operations are transmitted in the order submitted relative to RMA and atomic write operations. If not set, RMA and atomic reads may be transmitted ahead of RMA and atomic writes.

FI_ORDER_RAS : Read after send. If set, RMA and atomic read operations are transmitted in the order submitted relative to message send operations, including tagged sends. If not set, RMA and atomic reads may be transmitted ahead of sends.

FI_ORDER_WAR : Write after read. If set, RMA and atomic write operations are transmitted in the order submitted relative to RMA and atomic read operations. If not set, RMA and atomic writes may be transmitted ahead of RMA and atomic reads.

FI_ORDER_WAW : Write after write. If set, RMA and atomic write operations are transmitted in the order submitted relative to other RMA and atomic write operations. If not set, RMA and atomic writes may be transmitted out of order from their submission.

FI_ORDER_WAS : Write after send. If set, RMA and atomic write operations are transmitted in the order submitted relative to message send operations, including tagged sends. If not set, RMA and atomic writes may be transmitted ahead of sends.

FI_ORDER_SAR : Send after read. If set, message send operations, including tagged sends, are transmitted in order submitted relative to RMA and atomic read operations. If not set, message sends may be transmitted ahead of RMA and atomic reads.

FI_ORDER_SAW : Send after write. If set, message send operations, including tagged sends, are transmitted in order submitted relative to RMA and atomic write operations. If not set, message sends may be transmitted ahead of RMA and atomic writes.

FI_ORDER_SAS : Send after send. If set, message send operations, including tagged sends, are transmitted in the order submitted relative to other message send. If not set, message sends may be transmitted out of order from their submission.

comp_order - Completion Ordering

Completion ordering refers to the order in which completed requests are written into the completion queue. Completion ordering is similar to message order. Relaxed completion order may enable faster reporting of completed transfers, allow acknowledgments to be sent over different fabric paths, and support more sophisticated retry mechanisms. This can result in lower-latency completions, particularly when using unconnected endpoints. Strict completion ordering may require that providers queue completed operations or limit available optimizations.

For transmit requests, completion ordering depends on the endpoint communication type. For unreliable communication, completion ordering applies to all data transfer requests submitted to an endpoint. For reliable communication, completion ordering only applies to requests that target a single destination endpoint. Completion ordering of requests that target different endpoints over a reliable transport is not defined.

Applications should specify the completion ordering that they support or require. Providers should return the completion order that they actually provide, with the constraint that the returned ordering is stricter than that specified by the application. Supported completion order values are:

FI_ORDER_NONE : No ordering is defined for completed operations. Requests submitted to the transmit context may complete in any order.

FI_ORDER_STRICT : Requests complete in the order in which they are submitted to the transmit context.

inject_size

The requested inject operation size (see the FI_INJECT flag) that the context will support. This is the maximum size data transfer that can be associated with an inject operation (such as fi_inject) or may be used with the FI_INJECT data transfer flag.

size

The size of the context. The size is specified as the minimum number of transmit operations that may be posted to the endpoint without the operation returning -FI_EAGAIN.

iov_limit

This is the maximum number of IO vectors (scatter-gather elements) that a single posted operation may reference.

rma_iov_limit

This is the maximum number of RMA IO vectors (scatter-gather elements) that an RMA or atomic operation may reference. The rma_iov_limit corresponds to the rma_iov_count values in RMA and atomic operations. See struct fi_msg_rma and struct fi_msg_atomic in fi_rma.3 and fi_atomic.3, for additional details. This limit applies to both the number of RMA IO vectors that may be specified when initiating an operation from the local endpoint, as well as the maximum number of IO vectors that may be carried in a single request from a remote endpoint.

Receive Context Attributes

Attributes specific to the receive capabilities of an endpoint are specified using struct fi_rx_attr.

struct fi_rx_attr {
    uint64_t  caps;
    uint64_t  mode;
    uint64_t  op_flags;
    uint64_t  msg_order;
    uint64_t  comp_order;
    size_t    total_buffered_recv;
    size_t    size;
    size_t    iov_limit;
};

caps - Capabilities

The requested capabilities of the context. The capabilities must be a subset of those requested of the associated endpoint. See the CAPABILITIES section if fi_getinfo(3) for capability details. If the caps field is 0 on input to fi_getinfo(3), the caps value from the fi_info structure will be used.

mode

The operational mode bits of the context. The mode bits will be a subset of those associated with the endpoint. See the Mode section of fi_getinfo(3) for details. A mode value of 0 will be ignored on input to fi_getinfo(3), with the mode value of the fi_info structure used instead. On return from fi_getinfo(3), the mode will be set only to those constraints specific to receive operations.

op_flags - Default receive operation flags

Flags that control the operation of operations submitted against the context. Applicable flags are listed in the Operation Flags section.

msg_order - Message Ordering

For a description of message ordering, see the msg_order field in the Transmit Context Attribute section. Receive context message ordering defines the order in which received transport message headers are processed when received by an endpoint.

The following ordering flags, as defined for transmit ordering, also apply to the processing of received operations: FI_ORDER_NONE, FI_ORDER_RAR, FI_ORDER_RAW, FI_ORDER_RAS, FI_ORDER_WAR, FI_ORDER_WAW, FI_ORDER_WAS, FI_ORDER_SAR, FI_ORDER_SAW, and FI_ORDER_SAS.

comp_order - Completion Ordering

For a description of completion ordering, see the comp_order field in the Transmit Context Attribute section.

FI_ORDER_NONE : No ordering is defined for completed operations. Receive operations may complete in any order, regardless of their submission order.

FI_ORDER_STRICT : Receive operations complete in the order in which they are processed by the receive context, based on the receive side msg_order attribute.

FI_ORDER_DATA : When set, this bit indicates that received data is written into memory in order. Data ordering applies to memory accessed as part of a single operation and between operations if message ordering is guaranteed.

total_buffered_recv

Defines the total available space allocated by the provider to buffer messages that are received for which there is no matching receive operation. That is, this defines the minimal amount of receive side buffering available. If receive side buffering is disabled (total_buffered_recv = 0) and a message is received by an endpoint, then the behavior is dependent on whether resource management has been enabled (FI_RM_ENABLED has be set or not). See the Resource Management section of fi_domain.3 for further clarification.

size

The size of the context. The size is specified as the minimum number of receive operations that may be posted to the endpoint without the operation returning -FI_EAGAIN.

iov_limit

This is the maximum number of IO vectors (scatter-gather elements) that a single posted operating may reference.

Scalable Endpoints

A scalable endpoint is a communication portal that supports multiple transmit and receive contexts. Scalable endpoints are loosely modeled after the networking concept of transmit/receive side scaling, also known as multi-queue. Support for scalable endpoints is domain specific. Scalable endpoints may improve the performance of multi-threaded and parallel applications, by allowing threads to access independent transmit and receive queues. A scalable endpoint has a single transport level address, which can reduce the memory requirements needed to store remote addressing data, versus using standard endpoints. Scalable endpoints cannot be used directly for communication operations, and require the application to explicitly create transmit and receive contexts as described below.

fi_tx_context

Transmit contexts are independent transmit queues. Ordering and synchronization between contexts are not defined. Conceptually a transmit context behaves similar to a send-only endpoint. A transmit context may be configured with fewer attributes than the base endpoint, such as fewer capabilities, relaxed ordering, etc. Each transmit context has its own completion queue. The number of transmit contexts associated with an endpoint is specified during endpoint creation.

The fi_tx_context call is used to retrieve a specific context, identified by an index. Providers may dynamically allocate contexts when fi_tx_context is called, or may statically create all contexts when fi_endpoint is invoked. By default, a transmit context inherits the properties of its associated endpoint. However, applications may request context specific attributes through the attr parameter. Support for per transmit context attributes is provider specific and not guaranteed. Providers will return the actual attributes assigned to the context through the attr parameter, if provided.

fi_rx_context

Receive contexts are independent receive queues for receiving incoming data. Ordering and synchronization between contexts are not guaranteed. Conceptually a receive context behaves similar to a receive-only endpoint. A receive context may be configured with fewer attributes than the base endpoint, such as fewer capabilities, relaxed ordering, etc. Each receive context has its own completion queue. The number of receive contexts associated with an endpoint is specified during endpoint creation.

Receive contexts are often associated with steering flows, that specify which incoming packets targeting a scalable endpoint to process. However, receive contexts may be targeted directly by the initiator, if supported by the underlying protocol. Such contexts are referred to as 'named'. Support for named contexts must be indicated by setting the caps FI_NAMED_RX_CTX capability when the corresponding endpoint is created. Support for named receive contexts is coordinated with address vectors. See fi_av(3) and fi_rx_addr(3).

The fi_rx_context call is used to retrieve a specific context, identified by an index. Providers may dynamically allocate contexts when fi_rx_context is called, or may statically create all contexts when fi_endpoint is invoked. By default, a receive context inherits the properties of its associated endpoint. However, applications may request context specific attributes through the attr parameter. Support for per receive context attributes is provider specific and not guaranteed. Providers will return the actual attributes assigned to the context through the attr parameter, if provided.

Shared Contexts

Shared contexts are transmit and receive contexts explicitly shared among one or more endpoints. A shareable context allows an application to use a single dedicated provider resource among multiple transport addressable endpoints. This can greatly reduce the resources needed to manage communication over multiple endpoints by multiplexing transmit and/or receive processing, with the potential cost of serializing access across multiple endpoints. Support for shareable contexts is domain specific.

Conceptually, shareable transmit contexts are transmit queues that may be accessed by many endpoints. The use of a shared transmit context is mostly opaque to an application. Applications must allocate and bind shared transmit contexts to endpoints, but operations are posted directly to the endpoint. Shared transmit contexts are not associated with completion queues or counters. Completed operations are posted to the CQs bound to the endpoint. An endpoint may only be associated with a single shared transmit context.

Unlike shared transmit contexts, applications interact directly with shared receive contexts. Users post receive buffers directly to a shared receive context, with the buffers usable by any endpoint bound to the shared receive context. Shared receive contexts are not associated with completion queues or counters. Completed receive operations are posted to the CQs bound to the endpoint. An endpoint may only be associated with a single receive context, and all connectionless endpoints associated with a shared receive context must also share the same address vector.

Endpoints associated with a shared transmit context may use dedicated receive contexts, and vice-versa. Or an endpoint may use shared transmit and receive contexts. And there is no requirement that the same group of endpoints sharing a context of one type also share the context of an alternate type. Furthermore, an endpoint may use a shared context of one type, but a scalable set of contexts of the alternate type.

fi_stx_context

This call is used to open a shareable transmit context. See fi_tx_context call under the Scalable Endpoints section for details on the transit context attributes. The exception is that endpoints attached to a shared transmit context must use a subset of the transmit context attributes. This is opposite of the requirement for scalable endpoints.

fi_srx_context

This allocates a shareable receive context. See fi_rx_context call under Scalable Endpoints section for details on the receive context attributes. The exception is that endpoints attached to a shared receive context must use a subset of the receive context attributes. This is opposite of the requirement for scalable endpoints.

Operation Flags

Operation flags are obtained by OR-ing the following flags together. Operation flags define the default flags applied to an endpoint's data transfer operations, where a flags parameter is not available. Data transfer operations that take flags as input override the op_flags value of transmit or receive context attributes of an endpoint.

FI_INJECT : Indicates that all outbound data buffers should be returned to the user's control immediately after a data transfer call returns, even if the operation is handled asynchronously. This may require that the provider copy the data into a local buffer and transfer out of that buffer. A provider can limit the total amount of send data that may be buffered and/or the size of a single send that can use this flag. This limit is indicated using inject_size (see inject_size above).

FI_MULTI_RECV : Applies to posted receive operations. This flag allows the user to post a single buffer that will receive multiple incoming messages. Received messages will be packed into the receive buffer until the buffer has been consumed. Use of this flag may cause a single posted receive operation to generate multiple completions as messages are placed into the buffer. The placement of received data into the buffer may be subjected to provider specific alignment restrictions. The buffer will be returned to the application's control, and an FI_MULTI_RECV completion will be generated, when a message is received that cannot fit into the remaining free buffer space.

FI_COMPLETION : Indicates that a completion entry should be generated for data transfer operations.

FI_INJECT_COMPLETE : Indicates that a completion should be generated when the source buffer(s) may be reused. A completion guarantees that the buffers will not be read from again and the application may reclaim them. No other guarantees are made with respect to the state of the operation.

Note: This flag is used to control when a completion entry is inserted into a completion queue. It does not apply to operations that do not generate a completion queue entry, such as the fi_inject operation, and is not subject to the inject_size message limit restriction.

FI_TRANSMIT_COMPLETE : Indicates that a completion should be generated when the transmit operation has completed relative to the local provider. The exact behavior is dependent on the endpoint type.

For reliable endpoints:

Indicates that a completion should be generated when the operation has been delivered to the peer endpoint. A completion guarantees that the operation is no longer dependent on the fabric or local resources. The state of the operation at the peer endpoint is not defined.

For unreliable endpoints:

Indicates that a completion should be generated when the operation has been delivered to the fabric. A completion guarantees that the operation is no longer dependent on local resources. The state of the operation within the fabric is not defined.

FI_DELIVERY_COMPLETE : Indicates that a completion should not be generated until an operation has been processed by the destination endpoint(s). A completion guarantees that the result of the operation is available.

This completion mode applies only to reliable endpoints. For operations that return data to the initiator, such as RMA read or atomic-fetch, the source endpoint is also considered a destination endpoint. This is the default completion mode for such operations.

Notes

Users should call fi_close to release all resources allocated to the fabric endpoint.

Endpoints allocated with the FI_CONTEXT mode set must typically provide struct fi_context as their per operation context parameter. (See fi_getinfo.3 for details.) However, when FI_SELECTIVE_COMPLETION is enabled to suppress completion entries, and an operation is initiated without FI_COMPLETION flag set, then the context parameter is ignored. An application does not need to pass in a valid struct fi_context into such data transfers.

Operations that complete in error that are not associated with valid operational context will use the endpoint context in any error reporting structures.

Although applications typically associate individual completions with either completion queues or counters, an endpoint can be attached to both a counter and completion queue. When combined with using selective completions, this allows an application to use counters to track successful completions, with a CQ used to report errors. Operations that complete with an error increment the error counter and generate a completion event. The generation of entries going to the CQ can then be controlled using FI_SELECTIVE_COMPLETION.

As mentioned in fi_getinfo(3), the ep_attr structure can be used to query providers that support various endpoint attributes. fi_getinfo can return provider info structures that can support the minimal set of requirements (such that the application maintains correctness). However, it can also return provider info structures that exceed application requirements. As an example, consider an application requesting msg_order as FI_ORDER_NONE. The resulting output from getinfo may have all the ordering bits set. The application can reset the ordering bits it does not require before creating the endpoint. The provider is free to implement a stricter ordering than is required by the application.

Return Values

Returns 0 on success. On error, a negative value corresponding to fabric errno is returned. For fi_cancel, a return value of 0 indicates that the cancel request was submitted for processing.

Fabric errno values are defined in rdma/fi_errno.h.

Errors

-FI_EDOMAIN : A resource domain was not bound to the endpoint or an attempt was made to bind multiple domains.

-FI_ENOCQ : The endpoint has not been configured with necessary event queue.

-FI_EOPBADSTATE : The endpoint's state does not permit the requested operation.

See Also

fi_getinfo(3), fi_domain(3), fi_msg(3), fi_tagged(3), fi_rma(3)

Authors

OpenFabrics.

Referenced By

fabric(7), fi_atomic(3), fi_av(3), fi_cm(3), fi_cntr(3), fi_control(3), fi_cq(3), fi_direct(7), fi_domain(3), fi_eq(3), fi_fabric(3), fi_getinfo(3), fi_info(1), fi_mr(3), fi_msg(3), fi_pingpong(1), fi_rma(3), fi_tagged(3), fi_trigger(3).

fi_alias(3), fi_cancel(3), fi_enable(3), fi_ep(3), fi_ep_bind(3), fi_getopt(3), fi_passive_ep(3), fi_pep_bind(3), fi_rx_size_left(3), fi_scalable_ep_bind(3), fi_setopt(3) and fi_tx_size_left(3) are aliases of fi_endpoint(3).

2016-10-25 Libfabric Programmer's Manual Libfabric v1.4.0