Ubuntu Manpage: fi_verbs - The Verbs Fabric Provider

NAME

       fi_verbs - 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 up to
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.

AUTHORS

       OpenFabrics.