fi_domain - Man Page

Opens a fabric access domain, also referred to as a resource domain. Fabric domains are identified by a name. The properties of the opened domain are specified using the info parameter.

Similar to fi_domain, but accepts an extra parameter flags. Mainly used for opening peer domain. See fi_peer(3).

fi_open_ops is used to open provider specific interfaces. Provider interfaces may be used to access low-level resources and operations that are specific to the opened resource domain. The details of domain interfaces are outside the scope of this documentation.

fi_set_ops assigns callbacks that a provider should invoke in place of performing selected tasks. This allows users to modify or control a provider’s default behavior. Conceptually, it allows the user to hook specific functions used by a provider and replace it with their own.

The operations being modified are identified using a well-known character string, passed as the name parameter. The format of the ops parameter is dependent upon the name value. The ops parameter will reference a structure containing the callbacks and other fields needed by the provider to invoke the user’s functions.

If a provider accepts the override, it will return FI_SUCCESS. If the override is unknown or not supported, the provider will return -FI_ENOSYS. Overrides should be set prior to allocating resources on the domain.

The following fi_set_ops operations and corresponding callback structures are defined.

FI_SET_OPS_HMEM_OVERRIDE – Heterogeneous Memory Overrides

HMEM override allows users to override HMEM related operations a provider may perform. Currently, the scope of the HMEM override is to allow a user to define the memory movement functions a provider should use when accessing a user buffer. The user-defined memory movement functions need to account for all the different HMEM iface types a provider may encounter.

All objects allocated against a domain will inherit this override.

The following is the HMEM override operation name and structure.

#define FI_SET_OPS_HMEM_OVERRIDE "hmem_override_ops"

struct fi_hmem_override_ops {
    size_t  size;

    ssize_t (*copy_from_hmem_iov)(void *dest, size_t size,
        enum fi_hmem_iface iface, uint64_t device, const struct iovec *hmem_iov,
        size_t hmem_iov_count, uint64_t hmem_iov_offset);

    ssize_t (*copy_to_hmem_iov)(enum fi_hmem_iface iface, uint64_t device,
    const struct iovec *hmem_iov, size_t hmem_iov_count,
        uint64_t hmem_iov_offset, const void *src, size_t size);
};

All fields in struct fi_hmem_override_ops must be set (non-null) to a valid value.

size

This should be set to the sizeof(struct fi_hmem_override_ops). The size field is used for forward and backward compatibility purposes.

copy_from_hmem_iov

Copy data from the device/hmem to host memory. This function should return a negative fi_errno on error, or the number of bytes copied on success.

copy_to_hmem_iov

Copy data from host memory to the device/hmem. This function should return a negative fi_errno on error, or the number of bytes copied on success.

Associates an event queue with the domain. An event queue bound to a domain will be the default EQ associated with asynchronous control events that occur on the domain or active endpoints allocated on a domain. This includes CM events. Endpoints may direct their control events to alternate EQs by binding directly with the EQ.

Binding an event queue to a domain with the FI_REG_MR flag indicates that the provider should perform all memory registration operations asynchronously, with the completion reported through the event queue. If an event queue is not bound to the domain with the FI_REG_MR flag, then memory registration requests complete synchronously.

See fi_av_bind(3), fi_ep_bind(3), fi_mr_bind(3), fi_pep_bind(3), and fi_scalable_ep_bind(3) for more information.

The fi_close call is used to release all resources associated with a domain or interface. All objects associated with the opened domain must be released prior to calling fi_close, otherwise the call will return -FI_EBUSY.

On input to fi_getinfo, a user may set this to an opened domain instance to restrict output to the given domain. On output from fi_getinfo, if no domain was specified, but the user has an opened instance of the named domain, this will reference the first opened instance. If no instance has been opened, this field will be NULL.

The domain instance returned by fi_getinfo should only be considered valid if the application does not close any domain instances from another thread while fi_getinfo is being processed.

The name of the access domain.

The threading model specifies the level of serialization required of an application when using the libfabric data transfer interfaces. Control interfaces are always considered thread safe unless the control progress model is FI_PROGRESS_CONTROL_UNIFIED. A thread safe control interface allows multiple threads to progress the control interface, and (depending on threading model selected) one or more threads to progress the data interfaces at the same time. Applications which can guarantee serialization in their access of provider allocated resources and interfaces enable a provider to eliminate lower-level locks.

FI_THREAD_COMPLETION

The completion threading model is best suited for multi-threaded applications using scalable endpoints which desire lockless operation. Applications must serialize access to all objects that are associated by a common completion mechanism (for example, endpoints bound to the same CQ or counter). It is recommended that providers which support scalable endpoints also support this threading model.

Applications wanting to leverage FI_THREAD_COMPLETION should allocate transmit contexts, receive contexts, and completion queues and counters to individual threads.

FI_THREAD_DOMAIN

A domain serialization model requires applications to serialize access to all objects belonging to a domain.

FI_THREAD_ENDPOINT

The endpoint threading model is similar to FI_THREAD_FID, but with the added restriction that serialization is required when accessing the same endpoint, even if multiple transmit and receive contexts are used. Conceptually, FI_THREAD_ENDPOINT maps well to providers that implement fabric services in hardware but use a single command queue to access different data flows.

FI_THREAD_FID

A fabric descriptor (FID) serialization model requires applications to serialize access to individual fabric resources associated with data transfer operations and completions. Multiple threads must be serialized when accessing the same endpoint, transmit context, receive context, completion queue, counter, wait set, or poll set. Serialization is required only by threads accessing the same object.

For example, one thread may be initiating a data transfer on an endpoint, while another thread reads from a completion queue associated with the endpoint.

Serialization to endpoint access is only required when accessing the same endpoint data flow. Multiple threads may initiate transfers on different transmit contexts of the same endpoint without serializing, and no serialization is required between the submission of data transmit requests and data receive operations.

In general, FI_THREAD_FID allows the provider to be implemented without needing internal locking when handling data transfers. Conceptually, FI_THREAD_FID maps well to providers that implement fabric services in hardware and provide separate command queues to different data flows.

FI_THREAD_SAFE

A thread safe serialization model allows a multi-threaded application to access any allocated resources through any interface without restriction. All providers are required to support FI_THREAD_SAFE.

FI_THREAD_UNSPEC

This value indicates that no threading model has been defined. It may be used on input hints to the fi_getinfo call. When specified, providers will return a threading model that allows for the greatest level of parallelism.

Progress is the ability of the underlying implementation to complete processing of an asynchronous request. In many cases, the processing of an asynchronous request requires the use of the host processor. For example, a received message may need to be matched with the correct buffer, or a timed out request may need to be retransmitted. For performance reasons, it may be undesirable for the provider to allocate a thread for this purpose, which will compete with the application threads.

Control progress indicates the method that the provider uses to make progress on asynchronous control operations. Control operations are functions which do not directly involve the transfer of application data between endpoints. They include address vector, memory registration, and connection management routines.

Data progress indicates the method that the provider uses to make progress on data transfer operations. This includes message queue, RMA, tagged messaging, and atomic operations, along with their completion processing.

Progress frequently requires action being taken at both the transmitting and receiving sides of an operation. This is often a requirement for reliable transfers, as a result of retry and acknowledgement processing.

To balance between performance and ease of use, the following progress models are defined.

FI_PROGRESS_AUTO

This progress model indicates that the provider will make forward progress on an asynchronous operation without further intervention by the application. When FI_PROGRESS_AUTO is provided as output to fi_getinfo in the absence of any progress hints, it often indicates that the desired functionality is implemented by the provider hardware or is a standard service of the operating system.

It is recommended that providers support FI_PROGRESS_AUTO. However, if a provider does not natively support automatic progress, forcing the use of FI_PROGRESS_AUTO may result in threads being allocated below the fabric interfaces.

Note that prior versions of the library required providers to support FI_PROGRESS_AUTO. However, in some cases progress threads cannot be blocked when communication is idle, which results in threads spinning in progress functions. As a result, those providers only supported FI_PROGRESS_MANUAL.

FI_PROGRESS_MANUAL

This progress model indicates that the provider requires the use of an application thread to complete an asynchronous request. When manual progress is set, the provider will attempt to advance an asynchronous operation forward when the application attempts to wait on or read an event queue, completion queue, or counter where the completed operation will be reported. Progress also occurs when the application processes a poll or wait set that has been associated with the event or completion queue.

Only wait operations defined by the fabric interface will result in an operation progressing. Operating system or external wait functions, such as select, poll, or pthread routines, cannot.

Manual progress requirements not only apply to endpoints that initiate transmit operations, but also to endpoints that may be the target of such operations. This holds true even if the target endpoint will not generate completion events for the operations. For example, an endpoint that acts purely as the target of RMA or atomic operations that uses manual progress may still need application assistance to process received operations.

FI_PROGRESS_CONTROL_UNIFIED

This progress model indicates that the user will synchronize progressing the data and control operations themselves (i.e. this allows the control interface to NOT be thread safe). It is only valid for control progress (not data progress). Setting control=FI_PROGRESS_CONTROL_UNIFIED, data=FI_PROGRESS_MANUAL, and threading=FI_THREAD_DOMAIN/FI_THREAD_COMPLETION allows Libfabric to remove all locking in the critical data progress path.

FI_PROGRESS_UNSPEC

This value indicates that no progress model has been defined. It may be used on input hints to the fi_getinfo call.

Resource management (RM) is provider and protocol support to protect against overrunning local and remote resources. This includes local and remote transmit contexts, receive contexts, completion queues, and source and target data buffers.

When enabled, applications are given some level of protection against overrunning provider queues and local and remote data buffers. Such support may be built directly into the hardware and/or network protocol, but may also require that checks be enabled in the provider software. By disabling resource management, an application assumes all responsibility for preventing queue and buffer overruns, but doing so may allow a provider to eliminate internal synchronization calls, such as atomic variables or locks.

It should be noted that even if resource management is disabled, the provider implementation and protocol may still provide some level of protection against overruns. However, such protection is not guaranteed. The following values for resource management are defined.

FI_RM_DISABLED

The provider is free to select an implementation and protocol that does not protect against resource overruns. The application is responsible for resource protection.

FI_RM_ENABLED

Resource management is enabled for this provider domain.

FI_RM_UNSPEC

This value indicates that no resource management model has been defined. It may be used on input hints to the fi_getinfo call.

The behavior of the various resource management options depends on whether the endpoint is reliable or unreliable, as well as provider and protocol specific implementation details, as shown in the following table. The table assumes that all peers enable or disable RM the same.

The resource column indicates the resource being accessed by a data transfer operation.

Tx Ctx / Rx Ctx

Refers to the transmit/receive contexts when a data transfer operation is submitted. When RM is enabled, attempting to submit a request will fail if the context is full. If RM is disabled, an undefined error (provider specific) will occur. Such errors should be considered fatal to the context, and applications must take steps to avoid queue overruns.

Tx CQ / Rx CQ

Refers to the completion queue associated with the Tx or Rx context when a local operation completes. When RM is disabled, applications must take care to ensure that completion queues do not get overrun. When an overrun occurs, an undefined, but fatal, error will occur affecting all endpoints associated with the CQ. Overruns can be avoided by sizing the CQs appropriately or by deferring the posting of a data transfer operation unless CQ space is available to store its completion. When RM is enabled, providers may use different mechanisms to prevent CQ overruns. This includes failing (returning -FI_EAGAIN) the posting of operations that could result in CQ overruns, or internally retrying requests (which will be hidden from the application). See notes at the end of this section regarding CQ resource management restrictions.

Target EP / No Rx Buffer

Target EP refers to resources associated with the endpoint that is the target of a transmit operation. This includes the target endpoint’s receive queue, posted receive buffers (no Rx buffers), the receive side completion queue, and other related packet processing queues. The defined behavior is that seen by the initiator of a request. For FI_EP_DGRAM endpoints, if the target EP queues are unable to accept incoming messages, received messages will be dropped. For reliable endpoints, if RM is disabled, the transmit operation will complete in error. A provider may choose to return an error completion with the error code FI_ENORX for that transmit operation so that it can be retried. If RM is enabled, the provider will internally retry the operation.

Rx Buffer Overrun

This refers to buffers posted to receive incoming tagged or untagged messages, with the behavior defined from the viewpoint of the sender. The behavior for handling received messages that are larger than the buffers provided by the application is provider specific. Providers may either truncate the message and report a successful completion, or fail the operation. For datagram endpoints, failed sends will result in the message being dropped. For reliable endpoints, send operations may complete successfully, yet be truncated at the receive side. This can occur when the target side buffers received data until an application buffer is made available. The completion status may also be dependent upon the completion model selected byt the application (e.g. FI_DELIVERY_COMPLETE versus FI_TRANSMIT_COMPLETE).

Unmatched RMA / RMA Overrun

Unmatched RMA and RMA overruns deal with the processing of RMA and atomic operations. Unlike send operations, RMA operations that attempt to access a memory address that is either not registered for such operations, or attempt to access outside of the target memory region will fail, resulting in a transmit error.

When a resource management error occurs on an endpoint, the endpoint is transitioned into a disabled state. Any operations which have not already completed will fail and be discarded. For connectionless endpoints, the endpoint must be re-enabled before it will accept new data transfer operations. For connected endpoints, the connection is torn down and must be re-established.

There is one notable restriction on the protections offered by resource management. This occurs when resource management is enabled on an endpoint that has been bound to completion queue(s) using the FI_SELECTIVE_COMPLETION flag. Operations posted to such an endpoint may specify that a successful completion should not generate a entry on the corresponding completion queue. (I.e. the operation leaves the FI_COMPLETION flag unset). In such situations, the provider is not required to reserve an entry in the completion queue to handle the case where the operation fails and does generate a CQ entry, which would effectively require tracking the operation to completion. Applications concerned with avoiding CQ overruns in the occurrence of errors must ensure that there is sufficient space in the CQ to report failed operations. This can typically be achieved by sizing the CQ to at least the same size as the endpoint queue(s) that are bound to it.

Specifies the type of address vectors that are usable with this domain. For additional details on AV type, see fi_av(3). The following values may be specified.

FI_AV_MAP

Only address vectors of type AV map are requested or supported.

FI_AV_TABLE

Only address vectors of type AV index are requested or supported.

FI_AV_UNSPEC

Any address vector format is requested and supported.

Address vectors are only used by connectionless endpoints. Applications that require the use of a specific type of address vector should set the domain attribute av_type to the necessary value when calling fi_getinfo. The value FI_AV_UNSPEC may be used to indicate that the provider can support either address vector format. In this case, a provider may return FI_AV_UNSPEC to indicate that either format is supportable, or may return another AV type to indicate the optimal AV type supported by this domain.

Defines memory registration specific mode bits used with this domain. Full details on MR mode options are available in fi_mr(3). The following values may be specified.

FI_MR_ALLOCATED

Indicates that memory registration occurs on allocated data buffers, and physical pages must back all virtual addresses being registered.

FI_MR_COLLECTIVE

Requires data buffers passed to collective operations be explicitly registered for collective operations using the FI_COLLECTIVE flag.

FI_MR_ENDPOINT

Memory registration occurs at the endpoint level, rather than domain.

FI_MR_LOCAL

The provider is optimized around having applications register memory for locally accessed data buffers. Data buffers used in send and receive operations and as the source buffer for RMA and atomic operations must be registered by the application for access domains opened with this capability.

FI_MR_MMU_NOTIFY

Indicates that the application is responsible for notifying the provider when the page tables referencing a registered memory region may have been updated.

FI_MR_PROV_KEY

Memory registration keys are selected and returned by the provider.

FI_MR_RAW

The provider requires additional setup as part of their memory registration process. This mode is required by providers that use a memory key that is larger than 64-bits.

FI_MR_RMA_EVENT

Indicates that the memory regions associated with completion counters must be explicitly enabled after being bound to any counter.

FI_MR_UNSPEC

Defined for compatibility – library versions 1.4 and earlier. Setting mr_mode to 0 indicates that FI_MR_BASIC or FI_MR_SCALABLE are requested and supported.

FI_MR_VIRT_ADDR

Registered memory regions are referenced by peers using the virtual address of the registered memory region, rather than a 0-based offset.

FI_MR_BASIC

Defined for compatibility – library versions 1.4 and earlier. Only basic memory registration operations are requested or supported. This mode is equivalent to the FI_MR_VIRT_ADDR, FI_MR_ALLOCATED, and FI_MR_PROV_KEY flags being set in later library versions. This flag may not be used in conjunction with other mr_mode bits.

FI_MR_SCALABLE

Defined for compatibility – library versions 1.4 and earlier. Only scalable memory registration operations are requested or supported. Scalable registration uses offset based addressing, with application selectable memory keys. For library versions 1.5 and later, this is the default if no mr_mode bits are set. This flag may not be used in conjunction with other mr_mode bits.

Buffers used in data transfer operations may require notifying the provider of their use before a data transfer can occur. The mr_mode field indicates the type of memory registration that is required, and when registration is necessary. Applications that require the use of a specific registration mode should set the domain attribute mr_mode to the necessary value when calling fi_getinfo. The value FI_MR_UNSPEC may be used to indicate support for any registration mode.

Size of the memory region remote access key, in bytes. Applications that request their own MR key must select a value within the range specified by this value. Key sizes larger than 8 bytes require using the FI_RAW_KEY mode bit.

Applications may include a small message with a data transfer that is placed directly into a remote completion queue as part of a completion event. This is referred to as remote CQ data (sometimes referred to as immediate data). This field indicates the number of bytes that the provider supports for remote CQ data. If supported (non-zero value is returned), the minimum size of remote CQ data must be at least 4-bytes.

The optimal number of completion queues supported by the domain, relative to any specified or default CQ attributes. The cq_cnt value may be a fixed value of the maximum number of CQs supported by the underlying hardware, or may be a dynamic value, based on the default attributes of an allocated CQ, such as the CQ size and data format.

The total number of endpoints supported by the domain, relative to any specified or default endpoint attributes. The ep_cnt value may be a fixed value of the maximum number of endpoints supported by the underlying hardware, or may be a dynamic value, based on the default attributes of an allocated endpoint, such as the endpoint capabilities and size. The endpoint count is the number of addressable endpoints supported by the provider. Providers return capability limits based on configured hardware maximum capabilities. Providers cannot predict all possible system limitations without posteriori knowledge acquired during runtime that will further limit these hardware maximums (e.g. application memory consumption, FD usage, etc.).

The number of outbound command queues optimally supported by the provider. For a low-level provider, this represents the number of command queues to the hardware and/or the number of parallel transmit engines effectively supported by the hardware and caches. Applications which allocate more transmit contexts than this value will end up sharing underlying resources. By default, there is a single transmit context associated with each endpoint, but in an advanced usage model, an endpoint may be configured with multiple transmit contexts.

The number of inbound processing queues optimally supported by the provider. For a low-level provider, this represents the number hardware queues that can be effectively utilized for processing incoming packets. Applications which allocate more receive contexts than this value will end up sharing underlying resources. By default, a single receive context is associated with each endpoint, but in an advanced usage model, an endpoint may be configured with multiple receive contexts.

The maximum number of transmit contexts that may be associated with an endpoint.

The maximum number of receive contexts that may be associated with an endpoint.

The maximum number of endpoints that may be associated with a shared transmit context.

The maximum number of endpoints that may be associated with a shared receive context.

The optimal number of completion counters supported by the domain. The cq_cnt value may be a fixed value of the maximum number of counters supported by the underlying hardware, or may be a dynamic value, based on the default attributes of the domain.

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

Domain level capabilities. Domain capabilities indicate domain level features that are supported by the provider.

The following are support primary capabilities: FI_DIRECTED_RECV : When the domain is configured with FI_DIRECTED_RECV and FI_AV_AUTH_KEY, memory regions can be limited to specific authorization keys.

FI_AV_USER_ID

Indicates that the domain supports the ability to open address vectors with the FI_AV_USER_ID flag. If this domain capability is not set, address vectors cannot be opened with FI_AV_USER_ID. Note that FI_AV_USER_ID can still be supported through the AV insert calls without this domain capability set. See fi_av(3).

The following are supported secondary capabilities:

FI_LOCAL_COMM

At a conceptual level, this field indicates that the underlying device supports loopback communication. More specifically, this field indicates that an endpoint may communicate with other endpoints that are allocated from the same underlying named domain. If this field is not set, an application may need to use an alternate domain or mechanism (e.g. shared memory) to communicate with peers that execute on the same node.

FI_REMOTE_COMM

This field indicates that the underlying provider supports communication with nodes that are reachable over the network. If this field is not set, then the provider only supports communication between processes that execute on the same node – a shared memory provider, for example.

FI_SHARED_AV

Indicates that the domain supports the ability to share address vectors among multiple processes using the named address vector feature.

See fi_getinfo(3) for a discussion on primary versus secondary capabilities.

The default authorization key to associate with endpoint and memory registrations created within the domain. This field is ignored unless the fabric is opened with API version 1.5 or greater.

If domain auth_key_size is set to the value FI_AV_AUTH_KEY, auth_key must be NULL.

The length in bytes of the default authorization key for the domain. If set to 0, then no authorization key will be associated with endpoints and memory registrations created within the domain unless specified in the endpoint or memory registration attributes. This field is ignored unless the fabric is opened with API version 1.5 or greater.

If the size is set to the value FI_AV_AUTH_KEY, all endpoints and memory regions will be configured to use authorization keys associated with the AV. Providers which support authorization keys and connectionless endpoint must support this option.

: The maximum amount of error data, in bytes, that may be returned as part of a completion or event queue error. This value corresponds to the err_data_size field in struct fi_cq_err_entry and struct fi_eq_err_entry.

The optimal number of memory regions supported by the domain, or endpoint if the mr_mode FI_MR_ENDPOINT bit has been set. The mr_cnt value may be a fixed value of the maximum number of MRs supported by the underlying hardware, or may be a dynamic value, based on the default attributes of the domain, such as the supported memory registration modes. Applications can set the mr_cnt on input to fi_getinfo, in order to indicate their memory registration requirements. Doing so may allow the provider to optimize any memory registration cache or lookup tables.

This specifies the default traffic class that will be associated any endpoints created within the domain. See fi_endpoint(3) for additional information.

: The maximum number of authorization keys which can be supported per connectionless endpoint.