Provided by: libfabric-dev_1.5.3-1_amd64 
NAME
fi_domain - Open a fabric access domain
SYNOPSIS
#include <rdma/fabric.h>
#include <rdma/fi_domain.h>
int fi_domain(struct fid_fabric *fabric, struct fi_info *info,
struct fid_domain **domain, void *context);
int fi_close(struct fid *domain);
int fi_domain_bind(struct fid_domain *domain, struct fid *eq,
uint64_t flags);
int fi_open_ops(struct fid *domain, const char *name, uint64_t flags,
void **ops, void *context);
ARGUMENTS
fabric : Fabric domain
info : Fabric information, including domain capabilities and attributes.
domain : An opened access domain.
context : User specified context associated with the domain. This context is returned as
part of any asynchronous event associated with the domain.
eq : Event queue for asynchronous operations initiated on the domain.
name : Name associated with an interface.
ops : Fabric interface operations.
DESCRIPTION
An access domain typically refers to a physical or virtual NIC or hardware port; however,
a domain may span across multiple hardware components for fail-over or data striping
purposes. A domain defines the boundary for associating different resources together.
Fabric resources belonging to the same domain may share resources.
fi_domain
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.
fi_open_ops
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_domain_bind
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.
fi_close
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.
DOMAIN ATTRIBUTES
The fi_domain_attr structure defines the set of attributes associated with a domain.
struct fi_domain_attr {
struct fid_domain *domain;
char *name;
enum fi_threading threading;
enum fi_progress control_progress;
enum fi_progress data_progress;
enum fi_resource_mgmt resource_mgmt;
enum fi_av_type av_type;
int mr_mode;
size_t mr_key_size;
size_t cq_data_size;
size_t cq_cnt;
size_t ep_cnt;
size_t tx_ctx_cnt;
size_t rx_ctx_cnt;
size_t max_ep_tx_ctx;
size_t max_ep_rx_ctx;
size_t max_ep_stx_ctx;
size_t max_ep_srx_ctx;
size_t cntr_cnt;
size_t mr_iov_limit;
uint64_t caps;
uint64_t mode;
uint8_t *auth_key;
size_t auth_key_size;
size_t max_err_data;
size_t mr_cnt;
};
domain
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.
Name
The name of the access domain.
Multi-threading Support (threading)
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, and may be accessed by multiple threads. Applications which can guarantee
serialization in their access of provider allocated resources and interfaces enables a
provider to eliminate lower-level locks.
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.
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_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_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_COMPLETION : The completion threading model is intended for providers that make
use of manual progress. Applications must serialize access to all objects that are
associated through the use of having a shared completion structure. This includes
endpoint, completion queue, counter, wait set, and poll set objects.
For example, threads must serialize access to an endpoint and its bound completion
queue(s) and/or counters. Access to endpoints that share the same completion queue must
also be serialized.
The use of FI_THREAD_COMPLETION can increase parallelism over FI_THREAD_SAFE, but requires
the use of isolated resources.
FI_THREAD_DOMAIN : A domain serialization model requires applications to serialize access
to all objects belonging to a domain.
Progress Models (control_progress / data_progress)
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.
To balance between performance and ease of use, two progress models are defined.
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.
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.
All providers are required to 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.
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.
Resource Management (resource_mgmt)
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_UNSPEC : This value indicates that no resource management model has been defined.
It may be used on input hints to the fi_getinfo call.
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.
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.
Resource DGRAM EP-no RM DGRAM EP-with RM RDM/MSG EP-no RM RDM/MSG EP-with
RM
───────────────────────────────────────────────────────────────────────────────────────────
Tx Ctx undefined error EAGAIN undefined error EAGAIN
Rx Ctx undefined error EAGAIN undefined error EAGAIN
Tx CQ undefined error EAGAIN undefined error EAGAIN
Rx CQ undefined error EAGAIN undefined error EAGAIN
Target EP dropped dropped transmit error retried
No Rx Buffer dropped dropped transmit error retried
Rx Buf Overrun truncate or drop truncate or drop truncate or truncate or
error error
Unmatched RMA not applicable not applicable transmit error transmit error
RMA Overrun not applicable not applicable transmit error transmit error
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. 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 unconnected 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.
AV Type (av_type)
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_UNSPEC : Any address vector format is requested and supported.
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.
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.
Memory Registration Mode (mr_mode)
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_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_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_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_ALLOCATED : Indicates that memory registration occurs on allocated data buffers, and
physical pages must back all virtual addresses being registered.
FI_MR_PROV_KEY : Memory registration keys are selected and returned by the provider.
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_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_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.
MR Key Size (mr_key_size)
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.
CQ Data Size (cq_data_size)
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.
Completion Queue Count (cq_cnt)
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.
Endpoint Count (ep_cnt)
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.
Transmit Context Count (tx_ctx_cnt)
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.
Receive Context Count (rx_ctx_cnt)
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.
Maximum Endpoint Transmit Context (max_ep_tx_ctx)
The maximum number of transmit contexts that may be associated with an endpoint.
Maximum Endpoint Receive Context (max_ep_rx_ctx)
The maximum number of receive contexts that may be associated with an endpoint.
Maximum Sharing of Transmit Context (max_ep_stx_ctx)
The maximum number of endpoints that may be associated with a shared transmit context.
Maximum Sharing of Receive Context (max_ep_srx_ctx)
The maximum number of endpoints that may be associated with a shared receive context.
Counter Count (cntr_cnt)
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.
MR IOV Limit (mr_iov_limit)
This is the maximum number of IO vectors (scatter-gather elements) that a single memory
registration operation may reference.
Capabilities (caps)
Domain level capabilities. Domain capabilities indicate domain level features that are
supported by the provider.
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. All domain
capabilities are considered secondary capabilities.
mode
The operational mode bit related to using the domain.
FI_RESTRICTED_COMP : This bit indicates that the domain limits completion queues and
counters to only be used with endpoints, transmit contexts, and receive contexts that have
the same set of capability flags.
Default authorization key (auth_key)
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.
Default authorization key length (auth_key_size)
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.
Max Error Data Size (max_err_data)
: 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.
Memory Regions Count (mr_cnt)
The optimal number of memory regions supported by the domain. 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.
RETURN VALUE
Returns 0 on success. On error, a negative value corresponding to fabric errno is
returned. Fabric errno values are defined in rdma/fi_errno.h.
NOTES
Users should call fi_close to release all resources allocated to the fabric domain.
The following fabric resources are associated with domains: active endpoints, memory
regions, completion event queues, and address vectors.
Domain attributes reflect the limitations and capabilities of the underlying hardware
and/or software provider. They do not reflect system limitations, such as the number of
physical pages that an application may pin or number of file descriptors that the
application may open. As a result, the reported maximums may not be achievable, even on a
lightly loaded systems, without an administrator configuring system resources
appropriately for the installed provider(s).
SEE ALSO
fi_getinfo(3), fi_endpoint(3), fi_av(3), fi_ep(3), fi_eq(3), fi_mr(3)
AUTHORS
OpenFabrics.