fi_verbs (7)
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:
- [bu]
- FI_LOCAL_MR for all applications.
- [bu]
- FI_RX_CQ_DATA for applications that want to use RMA. Applications must take responsibility of posting receives for any incoming CQ data.
- [bu]
- 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.
Msg Ordering
Verbs provider support the following messaging ordering on the TX side:
- [bu]
- Read after Read
- [bu]
- Read after Write
- [bu]
- Read after Send
- [bu]
- Write after Write
- [bu]
- Write after Send
- [bu]
- Send after Write
- [bu]
- Send after Send
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 not supported. Generic fi_mr_regattr is not supported. No support for binding memory regions to a counter.
Wait objects
Only FI_WAIT_FD wait object is supported. 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, FI_FENCE
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.
Unsupported features specific to RDM endpoints
The RDM support for verbs have the following limitations:
- [bu]
- Supports iovs of only size 1.
- [bu]
- Wait objects are not supported.
- [bu]
- Not thread safe.
Fork
The support for fork in the provider has the following limitations:
- [bu]
- Fabric resources like endpoint, CQ, EQ, etc. should not be used in the forked process.
- [bu]
- 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 RDM endpoints
I]FI_VERBS_IFACE] : The prefix or the full name of the network interface associated with the IB device (default: ib)
I]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).
I]FI_VERBS_RDM_BUFFER_SIZE] : The maximum size of a buffered operation (bytes) (default: platform specific).
I]FI_VERBS_RDM_RNDV_SEG_SIZE] : The segment size for zero copy protocols (bytes)(default: 1073741824).
I]FI_VERBS_RDM_CQREAD_BUNCH_SIZE] : The number of entries to be read from the verbs completion queue at a time (default: 8).
I]FI_VERBS_RDM_THREAD_TIMEOUT] : The wake up timeout of the helper thread (usec) (default: 100).
I]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
SEE ALSO
C]fabric](7), C]fi_provider](7),