Libfabric Programmer's Manual

fi_verbs(7) Libfabric Programmer's Manual

NAME

The Verbs Fabric Provider

OVERVIEW

The verbs provider enables applications using OFI to be run over any verbs hardware (Infiniband, iWarp, etc). It uses the Linux Verbs API for network transport and provides a translation of OFI calls to appropriate verbs API calls. It uses librdmacm for communication management and libibverbs for other control and data transfer operations.

SUPPORTED FEATURES

The verbs provider supports a subset of OFI features.

Endpoint types

FI_EP_MSG, FI_EP_RDM (Experimental support FI_MSG, FI_TAGGED, FI_RMA interfaces).

Endpoint capabilities and features

MSG endpoints

FI_MSG, FI_RMA, FI_ATOMIC and shared receive contexts.

RDM endpoints

FI_MSG, FI_TAGGED, FI_RMA

Modes

Verbs provider requires applications to support the following modes:

  • FI_LOCAL_MR for all applications.

  • FI_RX_CQ_DATA for applications that want to use RMA. Applications must take responsibility of posting receives for any incoming CQ data.

  • FI_CONTEXT for applications making uses of the experimental FI_EP_RDM capability.

Addressing Formats

Supported addressing formats include FI_SOCKADDR, FI_SOCKADDR_IN, FI_SOCKADDR_IN6, FI_SOCKADDR_IB

Progress

Verbs provider supports FI_PROGRESS_AUTO: Asynchronous operations make forward progress automatically.

Operation flags

Verbs provider supports FI_INJECT, FI_COMPLETION, FI_REMOTE_CQ_DATA, FI_TRANSMIT_COMPLETE.

Msg Ordering

Verbs provider support the following message ordering:

  • Read after Read

  • Read after Write

  • Read after Send

  • Write after Write

  • Write after Send

  • Send after Write

  • Send after Send

and the following completion ordering:

  • TX contexts: FI_ORDER_STRICT
  • RX contexts: FI_ORDER_DATA

Fork

Verbs provider supports the fork system call by default. See the limitations section for restrictions. It can be turned off by setting the FI_FORK_UNSAFE environment variable to “yes”. This can improve the performance of memory registrations but it also makes the use of fork unsafe.

LIMITATIONS

Memory Regions

Only FI_MR_BASIC mode is supported. Adding regions via s/g list is supported only upto s/g list size of 1. No support for binding memory regions to a counter.

Wait objects

Only FI_WAIT_FD wait object is supported only for FI_EP_MSG endpoint type. Wait sets are not supported.

Resource Management

Application has to make sure CQs are not overrun as this cannot be detected by the provider.

Unsupported Features

The following features are not supported in verbs provider:

Unsupported Endpoint types

FI_EP_DGRAM

Unsupported Capabilities

FI_NAMED_RX_CTX, FI_DIRECTED_RECV, FI_TRIGGER, FI_MULTI_RECV, FI_RMA_EVENT

Other unsupported features

Scalable endpoints, FABRIC_DIRECT

Unsupported features specific to MSG endpoints

  • Counters, FI_SOURCE, FI_TAGGED, FI_PEEK, FI_CLAIM, fi_cancel, fi_ep_alias, shared TX context, cq_readfrom operations.
  • Completion flags are not reported if a request posted to an endpoint completes in error.

Unsupported features specific to RDM endpoints

The RDM support for verbs have the following limitations:

  • Supports iovs of only size 1.

  • Wait objects are not supported.

  • Not thread safe.

Fork

The support for fork in the provider has the following limitations:

  • Fabric resources like endpoint, CQ, EQ, etc. should not be used in the forked process.
  • The memory registered using fi_mr_reg has to be page aligned since ibv_reg_mr marks the entire page that a memory region belongs to as not to be re-mapped when the process is forked (MADV_DONTFORK).

RUNTIME PARAMETERS

The verbs provider checks for the following environment variables.

Variables specific to MSG endpoints

FI_VERBS_TX_SIZE
Default maximum tx context size (default: 384)
FI_VERBS_RX_SIZE
Default maximum rx context size (default: 384)
FI_VERBS_TX_IOV_LIMIT
Default maximum tx iov_limit (default: 4)
FI_VERBS_RX_IOV_LIMIT
Default maximum rx iov_limit (default: 4)

Variables specific to RDM endpoints

FI_VERBS_IFACE
The prefix or the full name of the network interface associated with the IB device (default: ib)
FI_VERBS_RDM_BUFFER_NUM
The number of pre-registered buffers for buffered operations between the endpoints, must be a power of 2 (default: 8).
FI_VERBS_RDM_BUFFER_SIZE
The maximum size of a buffered operation (bytes) (default: platform specific).
FI_VERBS_RDM_RNDV_SEG_SIZE
The segment size for zero copy protocols (bytes)(default: 1073741824).
FI_VERBS_RDM_CQREAD_BUNCH_SIZE
The number of entries to be read from the verbs completion queue at a time (default: 8).
FI_VERBS_RDM_THREAD_TIMEOUT
The wake up timeout of the helper thread (usec) (default: 100).
FI_VERBS_RDM_EAGER_SEND_OPCODE
The operation code that will be used for eager messaging. Only IBV_WR_SEND and IBV_WR_RDMA_WRITE_WITH_IMM are supported. The last one is not applicable for iWarp. (default: IBV_WR_SEND)

Environment variables notes

The fi_info utility would give the up-to-date information on environment variables: fi_info -p verbs -e

Troubleshooting / Known issues

When running an app over verbs provider with valgrind, there may be reports of memory leak in functions from dependent libraries (e.g. libibverbs, librdmacm). These leaks are safe to ignore.

SEE ALSO

fabric(7), fi_provider(7),