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fi_mrail(7)		       Libfabric v1.15.1		   fi_mrail(7)

NAME
       fi_mrail	- The Multi-Rail Utility Provider

OVERVIEW
       The  mrail provider (ofi_mrail) is an utility provider that layers over
       an underlying provider to enable	the  use  of  multiple	network	 ports
       (rails).	 This increases	the total available bandwidth of an underlying
       provider.   The	current	status of mrail	provider is experimental - not
       all libfabric features are supported and	performance is not guaranteed.

REQUIREMENTS
   Requirements	for underlying provider
       mrail provider requires the underlying provider to support the  follow-
       ing capabilities	/ modes:

       • Buffered receive (FI_BUFFERED_RECV)

       • FI_SOURCE

       • FI_AV_TABLE

   Requirements	for applications
       Applications  need  to:	* Support FI_MR_RAW MR mode bit	to make	use of
       FI_RMA capability.  * Set FI_OFI_MRAIL_ADDR env variable	 (see  RUNTIME
       PARAMETERS section below).

SUPPORTED FEATURES
       Endpoint	types
	      The provider supports only FI_EP_RDM.

       Endpoint	capabilities
	      The  following  data  transfer  interface	 is supported: FI_MSG,
	      FI_TAGGED, FI_RMA.

       # LIMITATIONS
	      Limitations of the underlying provider may show up  as  that  of
	      mrail  provider.	 mrail	provider doesn't allow pass-through of
	      any mode bits to the underlying provider.

   Unsupported features
       The following are the major libfabric features that are not  supported.
       Any  other feature not listed in	"Supported features" can be assumed as
       unsupported.

       • FI_ATOMIC

       • Scalable endpoints

       • Shared	contexts

       • FABRIC_DIRECT

       • Multicast

       • Triggered operations

FUNCTIONALITY OVERVIEW
       For messages (FI_MSG, FI_TAGGED), the provider uses different  policies
       to  send	 messages  over	 one  or more rails based on message size (See
       FI_OFI_MRIAL_CONFIG in the RUNTIME PARAMETERS  section).	  Ordering  is
       guaranteed through the use of sequence numbers.

       For RMA,	the data is striped equally across all rails.

RUNTIME	PARAMETERS
       The ofi_mrail provider checks for the following environment variables.

       FI_OFI_MRAIL_ADDR
	      Comma delimited list of individual rail addresses.  Each address
	      can  be an address in FI_ADDR_STR	format,	a host name, an	IP ad-
	      dress, or	a netdev interface name.

       FI_OFI_MRAIL_ADDR_STRC
	      Deprecated.  Replaced by FI_OFI_MRAIL_ADDR.

       FI_OFI_MRAIL_CONFIG
	      Comma separated list of <max_size>:<policy> pairs, sorted	in as-
	      cending order of <max_size>.  Each pair indicated	the rail shar-
	      ing policy to be used for	messages up to the size	<max_size> and
	      not covered by all previous pairs.  The value of <policy>	can be
	      fixed (a fixed rail is used), round-robin	(one rail per message,
	      selected in round-robin fashion),	or striping  (striping	across
	      all     the    rails).	 The	default	   configuration    is
	      16384:fixed,ULONG_MAX:striping.  The value ULONG_MAX can be  in-
	      put as -1.

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

AUTHORS
       OpenFabrics.

Libfabric Programmer's Manual	  2021-03-22			   fi_mrail(7)

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