Ubuntu Manpage: fabric - Fabric Interface Library

NAME

       fabric - Fabric Interface Library

SYNOPSIS

              #include <rdma/fabric.h>

       Libfabric  is  a  high-performance fabric software library designed to provide low-latency
       interfaces to fabric hardware.

OVERVIEW

       Libfabric provides 'process direct  I/O'  to  application  software  communicating  across
       fabric  software  and  hardware.   Process  direct  I/O, historically referred to as RDMA,
       allows an application to  directly  access  network  resources  without  operating  system
       interventions.  Data transfers can occur directly to and from application memory.

       There are two components to the libfabric software:

       Fabric  Providers  : Conceptually, a fabric provider may be viewed as a local hardware NIC
       driver, though a provider is not limited by  this  definition.   The  first  component  of
       libfabric  is  a  general purpose framework that is capable of handling different types of
       fabric hardware.  All fabric hardware devices and their software drivers are  required  to
       support  this  framework.   Devices and the drivers that plug into the libfabric framework
       are referred to as fabric providers, or simply providers.  Provider details may  be  found
       in fi_provider(7).

       Fabric  Interfaces : The second component is a set of communication operations.  Libfabric
       defines several sets of communication functions that providers can  support.   It  is  not
       required  that providers implement all the interfaces that are defined; however, providers
       clearly indicate which interfaces they do support.

FABRIC INTERFACES

       The fabric interfaces are designed such that they are cohesive and not simply a  union  of
       disjoint  interfaces.   The  interfaces  are  logically  divided  into two groups: control
       interfaces and communication operations.  The control  interfaces  are  a  common  set  of
       operations  that  provide access to local communication resources, such as address vectors
       and event queues.  The communication operations expose particular models of  communication
       and  fabric  functionality,  such  as  message  queues,  remote  memory access, and atomic
       operations.  Communication operations are associated with fabric endpoints.

       Applications will typically use the control interfaces to discover local capabilities  and
       allocate  necessary  resources.   They  will  then  allocate and configure a communication
       endpoint to send and receive data, or perform other types of data transfers,  with  remote
       endpoints.

CONTROL INTERFACES

The control interfaces APIs provide applications access to network resources. This
involves listing all the interfaces available, obtaining the capabilities of the
interfaces and opening a provider.

fi_getinfo - Fabric Information : The fi_getinfo call is the base call used to discover
and request fabric services offered by the system. Applications can use this call to
indicate the type of communication that they desire. The results from fi_getinfo,
fi_info, are used to reserve and configure fabric resources.

fi_getinfo returns a list of fi_info structures. Each structure references a single
fabric provider, indicating the interfaces that the provider supports, along with a named
set of resources. A fabric provider may include multiple fi_info structures in the
returned list.

fi_fabric - Fabric Domain : A fabric domain represents a collection of hardware and
software resources that access a single physical or virtual network. All network ports on
a system that can communicate with each other through the fabric belong to the same fabric
domain. A fabric domain shares network addresses and can span multiple providers.
libfabric supports systems connected to multiple fabrics.

fi_domain - Access Domains : An access domain represents a single logical connection into
a fabric. It may map to a single physical or virtual NIC or a port. An access domain
defines the boundary across which fabric resources may be associated. Each access domain
belongs to a single fabric domain.

fi_endpoint - Fabric Endpoint : A fabric endpoint is a communication portal. An endpoint
may be either active or passive. Passive endpoints are used to listen for connection
requests. Active endpoints can perform data transfers. Endpoints are configured with
specific communication capabilities and data transfer interfaces.

fi_eq - Event Queue : Event queues, are used to collect and report the completion of
asynchronous operations and events. Event queues report events that are not directly
associated with data transfer operations.

fi_cq - Completion Queue : Completion queues are high-performance event queues used to
report the completion of data transfer operations.

fi_cntr - Event Counters : Event counters are used to report the number of completed
asynchronous operations. Event counters are considered light-weight, in that a completion
simply increments a counter, rather than placing an entry into an event queue.

fi_mr - Memory Region : Memory regions describe application local memory buffers. In
order for fabric resources to access application memory, the application must first grant
permission to the fabric provider by constructing a memory region. Memory regions are
required for specific types of data transfer operations, such as RMA transfers (see
below).

fi_av - Address Vector : Address vectors are used to map higher level addresses, such as
IP addresses, which may be more natural for an application to use, into fabric specific
addresses. The use of address vectors allows providers to reduce the amount of memory
required to maintain large address look-up tables, and eliminate expensive address
resolution and look-up methods during data transfer operations.

DATA TRANSFER INTERFACES

Fabric endpoints are associated with multiple data transfer interfaces. Each interface
set is designed to support a specific style of communication, with an endpoint allowing
the different interfaces to be used in conjunction. The following data transfer
interfaces are defined by libfabric.

fi_msg - Message Queue : Message queues expose a simple, message-based FIFO queue
interface to the application. Message data transfers allow applications to send and
receive data with message boundaries being maintained.

fi_tagged - Tagged Message Queues : Tagged message lists expose send/receive data transfer
operations built on the concept of tagged messaging. The tagged message queue is
conceptually similar to standard message queues, but with the addition of 64-bit tags for
each message. Sent messages are matched with receive buffers that are tagged with a
similar value.

fi_rma - Remote Memory Access : RMA transfers are one-sided operations that read or write
data directly to a remote memory region. Other than defining the appropriate memory
region, RMA operations do not require interaction at the target side for the data transfer
to complete.

fi_atomic - Atomic : Atomic operations can perform one of several operations on a remote
memory region. Atomic operations include well-known functionality, such as atomic-add and
compare-and-swap, plus several other pre-defined calls. Unlike other data transfer
interfaces, atomic operations are aware of the data formatting at the target memory
region.

LOGGING INTERFACE

Logging can be controlled using the FI_LOG_LEVEL, FI_LOG_PROV, and FI_LOG_SUBSYS
environment variables.

FI_LOG_LEVEL : FI_LOG_LEVEL controls the amount of logging data that is output. The
following log levels are defined.

• Warn : Warn is the least verbose setting and is intended for reporting errors or
warnings.

• Trace : Trace is more verbose and is meant to include non-detailed output helpful to
tracing program execution.

• Info : Info is high traffic and meant for detailed output.

• Debug : Debug is high traffic and is likely to impact application performance. Debug
output is only available if the library has been compiled with debugging enabled.

FI_LOG_PROV : The FI_LOG_PROV environment variable enables or disables logging from
specific providers. Providers can be enabled by listing them in a comma separated
fashion. If the list begins with the '^' symbol, then the list will be negated. By
default all providers are enabled.

Example: To enable logging from the psm and sockets provider: FI_LOG_PROV="psm,sockets"

Example: To enable logging from providers other than psm: FI_LOG_PROV="^psm"

FI_LOG_SUBSYS : The FI_LOG_SUBSYS environment variable enables or disables logging at the
subsystem level. The syntax for enabling or disabling subsystems is similar to that used
for FI_LOG_PROV. The following subsystems are defined.

• core : Provides output related to the core framework and its management of providers.

• fabric : Provides output specific to interactions associated with the fabric object.

• domain : Provides output specific to interactions associated with the domain object.

• ep_ctrl : Provides output specific to endpoint non-data transfer operations, such as CM
operations.

• ep_data : Provides output specific to endpoint data transfer operations.

• av : Provides output specific to address vector operations.

• cq : Provides output specific to completion queue operations.

• eq : Provides output specific to event queue operations.

• mr : Provides output specific to memory registration.

NOTES

       Because  libfabric  is  designed to provide applications direct access to fabric hardware,
       there are limits on how libfabric resources may be used in conjunction with system  calls.
       These  limitations  are  notable  for  developers  who  may be familiar programming to the
       sockets interface.  Although limits are  provider  specific,  the  following  restrictions
       apply  to  many  providers  and  should be adhered to by applications desiring portability
       across providers.

       fork : Fabric resources are not guaranteed to  be  available  by  child  processes.   This
       includes  objects,  such  as  endpoints  and  completion  queues,  as  well as application
       controlled data buffers which have been  assigned  to  the  network.   For  example,  data
       buffers  that  have  been  registered with a fabric domain may not be available in a child
       process because of copy on write restrictions.

AUTHORS

       OpenFabrics.