fi_hook - The Hook Fabric Provider Utility


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.


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 current 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:

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.


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 restricted 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 following counters are available:

Counts the number of CPU cycles each function takes to complete.
Counts the number of CPU instructions each function takes to complete. This is the default performance counter if none is specified.


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.


fabric(7), fi_provider(7)