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fi_efa - Man Page

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 for send and receive operations, i.e. it does not require FI_MR_LOCAL. Applications may specify FI_MR_LOCAL in the MR mode flags in order to use descriptors provided by the application. The FI_EP_DGRAM endpoint only supports FI_MR_LOCAL.


RDM and DGRAM endpoints support FI_PROGRESS_MANUAL. EFA erroneously claims the support for FI_PROGRESS_AUTO, despite not properly supporting automatic progress. Unfortunately, some Libfabric consumers also ask for FI_PROGRESS_AUTO when they only require FI_PROGRESS_MANUAL, and fixing this bug would break those applications. This will be fixed in a future version of the EFA provider by adding proper support for FI_PROGRESS_AUTO.


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 DGRAM endpoint 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 for the DGRAM endpoint.

No support for inject.

When using FI_HMEM for AWS Neuron or Habana SynapseAI buffers, the provider requires peer to peer transaction support between the EFA and the FI_HMEM device. Therefore, the FI_HMEM_P2P_DISABLED option is not supported by the EFA provider for AWS Neuron or Habana SynapseAI.

Provider Specific Endpoint Level Option


Defines the number of RNR retry. The application can use it to reset RNR retry counter via the call to fi_setopt. Note that this option must be set before the endpoint is enabled. Otherwise, the call will fail. Also note that this option only applies to RDM endpoint.


These options only apply to the fi_getopt() call. They are used to query the EFA provider to determine if the endpoint is emulating Read, Write, and Atomic operations (return value is true), or if these operations are assisted by hardware support (return value is false).


Only available if the application selects a libfabric API version >= 1.18. This option allows an application to change libfabric’s behavior with respect to RDMA transfers. Note that there is also an environment variable FI_EFA_USE_DEVICE_RDMA which the user may set as well. If the environment variable and the argument provided with this variable are in conflict, then fi_setopt will return -FI_EINVAL, and the environment variable will be respected. If the hardware does not support RDMA and the argument is true, then fi_setopt will return -FI_EOPNOTSUPP. If the application uses API version < 1.18, the argument is ignored and fi_setopt returns -FI_ENOPROTOOPT. The default behavior for RDMA transfers depends on API version. For API >= 1.18 RDMA is enabled by default on any hardware which supports it. For API<1.18, RDMA is enabled by default only on certain newer hardware revisions.


It is used to force the endpoint to use in-order send/recv operation for each 128 bytes aligned block. Enabling the option will guarantee data inside each 128 bytes aligned block being sent and received in order, it will also guarantee data to be delivered to the receive buffer only once. If endpoint is not able to support this feature, it will return -FI_EOPNOTSUPP for the call to fi_setopt().


It is used to set the endpoint to use in-order RDMA write operation for each 128 bytes aligned block. Enabling the option will guarantee data inside each 128 bytes aligned block being written in order, it will also guarantee data to be delivered to the target buffer only once. If endpoint is not able to support this feature, it will return -FI_EOPNOTSUPP for the call to fi_setopt().

Provider Specific Domain Ops

The efa provider exports extensions for operations that are not provided by the standard libfabric interface. These extensions are available via the “fi_ext_efa.h” header file.

Domain Operation Extension

Domain operation extension is obtained by calling fi_open_ops (see fi_domain(3))

int fi_open_ops(struct fid *domain, const char *name, uint64_t flags,
    void **ops, void *context);

and requesting FI_EFA_DOMAIN_OPS in name. fi_open_ops returns ops as the pointer to the function table fi_efa_ops_domain defined as follows:

struct fi_efa_ops_domain {
    int (*query_mr)(struct fid_mr *mr, struct fi_efa_mr_attr *mr_attr);

It contains the following operations


This op query an existing memory registration as input, and outputs the efa specific mr attribute which is defined as follows

struct fi_efa_mr_attr {
    uint16_t ic_id_validity;
    uint16_t recv_ic_id;
    uint16_t rdma_read_ic_id;
    uint16_t rdma_recv_ic_id;

Validity mask of interconnect id fields. Currently the following bits are supported in the mask:

FI_EFA_MR_ATTR_RECV_IC_ID: recv_ic_id has a valid value.

FI_EFA_MR_ATTR_RDMA_READ_IC_ID: rdma_read_ic_id has a valid value.

FI_EFA_MR_ATTR_RDMA_RECV_IC_ID: rdma_recv_ic_id has a valid value.


Physical interconnect used by the device to reach the MR for receive operation. It is only valid when ic_id_validity has the FI_EFA_MR_ATTR_RECV_IC_ID bit.


Physical interconnect used by the device to reach the MR for RDMA read operation. It is only valid when ic_id_validity has the FI_EFA_MR_ATTR_RDMA_READ_IC_ID bit.


Physical interconnect used by the device to reach the MR for RDMA write receive. It is only valid when ic_id_validity has the FI_EFA_MR_ATTR_RDMA_RECV_IC_ID bit.

Return value

query_mr() returns 0 on success, or the value of errno on failure (which indicates the failure reason).

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.

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


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.


Enable SHM provider to provide the communication across all intra-node processes. SHM transfer will be disabled in the case where ptrace protection is turned on. You can turn it off to enable shm transfer.

FI_EFA_ENABLE_SHM_TRANSFER is parsed during the fi_domain call and is related to the FI_OPT_SHARED_MEMORY_PERMITTED endpoint option. If FI_EFA_ENABLE_SHM_TRANSFER is set to true, the FI_OPT_SHARED_MEMORY_PERMITTED endpoint option overrides FI_EFA_ENABLE_SHM_TRANSFER. If FI_EFA_ENABLE_SHM_TRANSFER is set to false, but the FI_OPT_SHARED_MEMORY_PERMITTED is set to true, the FI_OPT_SHARED_MEMORY_PERMITTED setopt call will fail with -FI_EINVAL.


Defines the maximum number of entries in SHM provider’s address vector.


Defines the switch point between small/medium message and large message. The message larger than this switch point will be transferred with large message protocol. NOTE: This parameter is now deprecated.


The maximum size for inter EFA messages to be sent by using medium message protocol. Messages which can fit in one packet will be sent as eager message. Messages whose sizes are smaller than this value will be sent using medium message protocol. Other messages will be sent using CTS based long message protocol.


Enable fork() support. This may have a small performance impact and should only be set when required. Applications that require to register regions backed by huge pages and also require fork support are not supported.


The maximum number of bytes that will be eagerly sent by inflight messages uses runting read message protocol (Default 307200).


The minimum message size in bytes for inter EFA read message protocol. If instance support RDMA read, messages whose size is larger than this value will be sent by read message protocol. (Default 1048576).


The mimimum message size for emulated inter EFA write to use read write protocol. If firmware support RDMA read, and FI_EFA_USE_DEVICE_RDMA is 1, write requests whose size is larger than this value will use the read write protocol (Default 65536). If the firmware supports RDMA write, device RDMA write will always be used.


Specify whether to require or ignore RDMA features of the EFA device. - When set to 1/true/yes/on, all RDMA features of the EFA device are used. But if EFA device does not support RDMA and FI_EFA_USE_DEVICE_RDMA is set to 1/true/yes/on, user’s application is aborted and a warning message is printed. - When set to 0/false/no/off, libfabric will emulate all fi_rma operations instead of offloading them to the EFA network device. Libfabric will not use device RDMA to implement send/receive operations. - If not set, RDMA operations will occur when available based on RDMA device ID/version.


Specify Whether EFA provider can use huge page memory for internal buffer. Using huge page memory has a small performance advantage, but can cause system to run out of huge page memory. By default, EFA provider will use huge page unless FI_EFA_FORK_SAFE is set to 1/on/true.

See Also

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



Referenced By


2024-01-23 Libfabric Programmer’s Manual Libfabric v1.21.0