fi_efa man page

fi_efa ā€” The Amazon Elastic Fabric Adapter (EFA) Provider


The EFA provider supports the Elastic Fabric Adapter (EFA) device on Amazon EC2. EFA provides reliable and unreliable datagram send/receive with direct hardware access from userspace (OS bypass).

Supported Features

The following features are supported:

Endpoint types

The provider supports endpoint type FI_EP_DGRAM, and FI_EP_RDM on a new Scalable (unordered) Reliable Datagram protocol (SRD). SRD provides support for reliable datagrams and more complete error handling than typically seen with other Reliable Datagram (RD) implementations. The EFA provider provides segmentation, reassembly of out-of-order packets to provide send-after-send ordering guarantees to applications via its FI_EP_RDM endpoint.

RDM Endpoint capabilities

The following data transfer interfaces are supported via the FI_EP_RDM endpoint: FI_MSG, FI_TAGGED, and FI_RMA. FI_SEND, FI_RECV, FI_DIRECTED_RECV, FI_MULTI_RECV, and FI_SOURCE capabilities are supported. The endpoint provides send-after-send guarantees for data operations. The FI_EP_RDM endpoint does not have a maximum message size.

DGRAM Endpoint capabilities

The DGRAM endpoint only supports FI_MSG capability with a maximum message size of the MTU of the underlying hardware (approximately 8 KiB).

Address vectors

The provider supports FI_AV_TABLE and FI_AV_MAP address vector types. FI_EVENT is unsupported.

Completion events

The provider supports FI_CQ_FORMAT_CONTEXT, FI_CQ_FORMAT_MSG, and FI_CQ_FORMAT_DATA. FI_CQ_FORMAT_TAGGED is supported on the RDM endpoint. Wait objects are not currently supported.


The provider requires the use of FI_MSG_PREFIX when running over the DGRAM endpoint, and requires FI_MR_LOCAL for all memory registrations on the DGRAM endpoint.

Memory registration modes

The RDM endpoint does not require memory registration and the FI_EP_DGRAM endpoint only supports FI_MR_LOCAL.


The RDM endpoint supports both FI_PROGRESS_AUTO and FI_PROGRESS_MANUAL, with the default set to auto. However, receive side data buffers are not modified outside of completion processing routines. The DGRAM endpoint only supports FI_PROGRESS_MANUAL.


The RDM endpoint supports FI_THREAD_SAFE, the DGRAM endpoint supports FI_THREAD_DOMAIN, i.e. the provider is not thread safe when using the DGRAM endpoint.


The provider does not support FI_ATOMIC interfaces. For RMA operations, completion events for RMA targets (FI_RMA_EVENT) is not supported. The DGRAM endpoint does not fully protect against resource overruns, so resource management is disabled for this endpoint (FI_RM_DISABLED).

No support for selective completions.

No support for counters.

No support for inject.

Runtime Parameters


Maximum number of transmit operations before the provider returns -FI_EAGAIN. For only the RDM endpoint, this parameter will cause transmit operations to be queued when this value is set higher than the default and the transmit queue is full.


Maximum number of receive operations before the provider returns -FI_EAGAIN.


Maximum number of IOVs for a transmit operation.


Maximum number of IOVs for a receive operation.

Runtime Parameters Specific to RDM Endpoint

These OFI runtime parameters apply only to the RDM endpoint.


Maximum number of MTU-sized messages that can be in flight from any single endpoint as part of long message data transfer.


Depth of transmit queue opened with the NIC. This may not be set to a value greater than what the NIC supports.


Size of out of order reorder buffer (in messages). Messages received out of this window will result in an error.


Size of any cq created, in number of entries.


Enables using the mr cache and in-line registration instead of a bounce buffer for iov's larger than max_memcpy_size. Defaults to true. When disabled, only uses a bounce buffer


Enables merging overlapping and adjacent memory registration regions. Defaults to true.


Sets the maximum number of memory registrations that can be cached at any time.


Sets the maximum amount of memory that cached memory registrations can hold onto at any time.


Threshold size switch between using memory copy into a pre-registered bounce buffer and memory registration on the user buffer.


Overrides the default MTU size of the device.


Enables the use of a separate pool of bounce-buffers to copy unexpected messages out of the pre-posted receive buffers.


Enables the use of a separate pool of bounce-buffers to copy out-of-order RTS packets out of the pre-posted receive buffers.


Maximum timeout (us) for backoff to a peer after a receiver not ready error.


Time interval (us) for the base timeout to use for exponential backoff to a peer after a receiver not ready error.

See Also

fabric(7), fi_provider(7), fi_getinfo(3)



Referenced By


2019-06-15 Libfabric Programmer's Manual Libfabric v1.8.0