NAME

       fi_direct - Direct fabric provider access

SYNOPSIS

              -DFABRIC_DIRECT

              #define FABRIC_DIRECT

       Fabric  direct provides a mechanism for applications to compile against a specific fabric providers with‐
       out going through the libfabric framework or function vector tables.  This allows for  extreme  optimiza‐
       tion via function inlining at the cost of supporting multiple providers or different versions of the same
       provider.

DESCRIPTION

       The use of fabric direct is intended only for applications that require the absolute minimum software la‐
       tency,  and are willing to re-compile for specific fabric hardware.  Providers that support fabric direct
       implement their own versions of the static inline calls which are define in the libfabric  header  files,
       define  selected  enum values, and provide defines for compile-time optimizations.  Applications can then
       code against the standard libfabric calls, but link directly against the provider calls by defining  FAB‐
       RIC_DIRECT as part of their build.

       In  general,  the use of fabric direct does not require application source code changes, and, instead, is
       limited to the build process.

       Providers supporting fabric direct must install 'direct' versions of all  libfabric  header  files.   For
       convenience,  the  libfabric sources contain sample header files that may be modified by a provider.  The
       'direct' header file names have 'fi_direct' as their prefix: fi_direct.h, fi_direct_endpoint.h, etc.

       Direct providers are prohibited from overriding or modifying existing data structures.  However, provider
       specific extensions are still available.  In addition to provider direct function calls to provider code,
       a fabric direct provider may define zero of more of the following capability  definitions.   Applications
       can  check  for  these  capabilities  in  order to optimize code paths at compile time, versus relying on
       run-time checks.

CAPABILITY DEFINITIONS

       In order that application code may be optimized during compile time, direct providers must provide defin‐
       itions for various capabilities and modes, if those capabilities are supported.   The  following  #define
       values may be used by an application to test for provider support of supported features.

       FI_DIRECT_CONTEXT
              The  provider  sets FI_CONTEXT or FI_CONTEXT2 for fi_info:mode.  See fi_getinfo for additional de‐
              tails.  When FI_DIRECT_CONTEXT is defined, applications should use struct fi_context in their def‐
              initions, even if FI_CONTEXT2 is set.

       FI_DIRECT_LOCAL_MR
              The provider sets FI_LOCAL_MR for fi_info:mode.  See fi_getinfo for additional details.

SEE ALSO

       fi_getinfo(3), fi_endpoint(3), fi_domain(3)

AUTHORS

       OpenFabrics.

Libfabric Programmer's Manual                      2018-10-05                                       fi_direct(7)