Ubuntu Manpage: fi_verbs - The Verbs Fabric Provider

Provided by: libfabric-dev_1.6.2-3ubuntu0.1_amd64

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

New change in libfabric v1.6: FI_EP_RDM is supported through the OFI RxM utility provider. This is done
automatically when the app requests FI_EP_RDM endpoint. Please refer the man page for RxM provider to
learn more. The provider's internal support for RDM endpoints is deprecated and would be removed from
libfabric v1.7 onwards. Till then apps can explicitly request the internal RDM support by disabling
ofi_rxm provider through FI_PROVIDER env variable (FI_PROVIDER=^ofi_rxm).

Endpoint capabilities and features
MSG endpoints
FI_MSG, FI_RMA, FI_ATOMIC and shared receive contexts.

RDM endpoints (internal - deprecated)
FI_MSG, FI_TAGGED, FI_RMA

DGRAM endpoints
FI_MSG

Modes
Verbs provider requires applications to support the following modes:

FI_EP_MSG endpoint type
• FI_LOCAL_MR / FI_MR_LOCAL mr mode.

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

FI_EP_RDM endpoint type (internal - deprecated)
• FI_CONTEXT

Addressing Formats
Supported addressing formats include * MSG and RDM (internal - deprecated) EPs support: FI_SOCKADDR,
FI_SOCKADDR_IN, FI_SOCKADDR_IN6, FI_SOCKADDR_IB * DGRAM supports: FI_ADDR_IB_UD

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.

Memory Registration Cache
The verbs provider features a memory registration cache. This speeds up memory registration calls from
applications by caching registrations of frequently used memory regions. The user can control the
maximum combined size of all cache entries and the maximum number of cache entries with the environment
variables FI_VERBS_MR_MAX_CACHED_SIZE and FI_VERBS_MR_MAX_CACHED_CNT respectively. Look below in the
environment variables section for details.

Note: The memory registration cache framework hooks into alloc and free calls to monitor the memory
regions. If this doesn't work as expected caching would not be optimal.

LIMITATIONS

Memory Regions
Only FI_MR_BASIC mode is supported. Adding regions via s/g list is supported only up to a 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 Capabilities
FI_NAMED_RX_CTX, FI_DIRECTED_RECV, FI_TRIGGER, 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 (internal - deprecated)
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.

   Common variables:
       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).  Note: RDM (internal - deprecated)  EP
       type supports only 1

       FI_VERBS_RX_IOV_LIMIT  : Default maximum rx iov_limit (default: 4).  Note: RDM (internal - deprecated) EP
       type supports only 1

       FI_VERBS_INLINE_SIZE : Default maximum inline size.  Actual  inject  size  returned  in  fi_info  may  be
       greater (default: 64)

       FI_VERBS_MIN_RNR_TIMER : Set min_rnr_timer QP attribute (0 - 31) (default: 12)

       FI_VERBS_USE_ODP  : Enable On-Demand-Paging (ODP) experimental feature.  The feature is supported only on
       Mellanox OFED (default: 0)

       FI_VERBS_CQREAD_BUNCH_SIZE : The number of entries to be read from the verbs completion queue at  a  time
       (default: 8).

       FI_VERBS_IFACE  :  The  prefix or the full name of the network interface associated with the verbs device
       (default: ib)

       FI_VERBS_MR_CACHE_ENABLE : Enable Memory Registration caching (default: 0)

       FI_VERBS_MR_MAX_CACHED_CNT : Maximum number of cache entries (default: 4096)

       FI_VERBS_MR_MAX_CACHED_SIZE : Maximum total size of cache entries (default: 4 GB)

   Variables specific to RDM (internal - deprecated) endpoints
       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_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)

       FI_VERBS_RDM_CM_THREAD_AFFINITY  :  If  specified,  bind the CM thread to the indicated range(s) of Linux
       virtual   processor   ID(s).    This   option   is   currently   not   supported   on   OS   X.    Usage:
       id_start[-id_end[:stride]][,]

   Variables specific to DGRAM endpoints
       FI_VERBS_DGRAM_USE_NAME_SERVER  : The option that enables/disables OFI Name Server thread.  The NS thread
       is used to resolve IP-addresses to provider specific addresses (default: 1, if "OMPI_COMM_WORLD_RANK" and
       "PMI_RANK" environment variables aren't defined)

       FI_VERBS_NAME_SERVER_PORT  :  The  port  on  which  Name  Server  thread listens incoming connections and
       requests (default: 5678)

   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.