NAME

       fi_hook - The Hook Fabric Provider Utility

OVERVIEW

       The  hooking  provider is a utility function that can intercept calls to any provider.  The hook provider
       is always available, but has zero impact on calls unless enabled.  It is useful for providing performance
       data on selected calls or debugging information.

SUPPORTED FEATURES

       Hooking support is enabled through the FI_HOOK environment variable.  To enable hooking, FI_HOOK must  be
       set  to  the  name of one or more of the available hooking providers.  When multiple hooks are specified,
       the names must be separated by a semi-colon.  To obtain a list of hooking providers available on the cur‐
       rent system, one can use the fi_info utility with the `–env' command line option.  Hooking providers  are
       usually identified by `hook' appearing in the provider name.

       Known hooking providers include the following:

       ofi_hook_perf
              This  hooks  `fast  path' data operation calls.  Performance data is captured on call entrance and
              exit, in order to provide an average of how long each call takes to complete.  See the PERFORMANCE
              HOOKS section for available performance data.

PERFORMANCE HOOKS

       The hook provider allows capturing inline performance data by accessing the  CPU  Performance  Management
       Unit  (PMU).   PMU  data is only available on Linux systems.  Additionally, access to PMU data may be re‐
       stricted to privileged (super-user) applications.

       Performance data is captured for critical data transfer calls:  fi_msg,  fi_rma,  fi_tagged,  fi_cq,  and
       fi_cntr.  Captured data is displayed as logged data using the FI_LOG_LEVEL trace level.  Performance data
       is logged when the associated fabric is destroyed.

       The environment variable FI_PERF_CNTR is used to identify which performance counter is tracked.  The fol‐
       lowing counters are available:

       cpu_cycles
              Counts the number of CPU cycles each function takes to complete.

       cpu_instr
              Counts  the  number of CPU instructions each function takes to complete.  This is the default per‐
              formance counter if none is specified.

LIMITATIONS

       Hooking functionality is not available for providers built using the FI_FABRIC_DIRECT feature.  That  is,
       directly linking to a provider prevents hooking.

       The hooking provider does not work with triggered operations.  Application that use FI_TRIGGER operations
       that attempt to hook calls will likely crash.

SEE ALSO

       fabric(7), fi_provider(7)

AUTHORS

       OpenFabrics.

Libfabric Programmer’s Manual                      2022-12-11                                         fi_hook(7)