Reference Implmentation of the Process Management Interface Exascale (PMIx) standard

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The granularity of debugging output from PMIx depends greatly on the version being used. In all cases, maximum output is available when PMIx is configured with –enable-debug, though installations built that way should not be used in general production or performance testing as it does impact the performance of the library.

Debugging PMIx v1.x The early releases of PMIx have only one debugging option, though there are different levels available for it. Debugging output is controlled via the PMIX_DEBUG environmental parameter using a range of 0-100. A value of 2 will provide a degree of tracing through the code base (though this wasn’t rigidly enforced), while higher values will trigger more detailed output from inside the infrastructure itself.

Debugging PMIx v2.x Beginning with the v2.0 release, PMIx switched to a plugin-based architecture using the Modular Component Architecture (MCA) plugin manager developed by Jeff Squyres et al at Indiana University in the early 2000s. MCA is specifically designed to provide generalized plugin support in high-performance environments, with low overhead and minimal latency impact. In PMIx, MCA is used to define general abstraction interfaces (known as “frameworks”) that capture a certain range of functionality – e.g., a framework for handling buffer-based pack/unpack operations, or one that supports security protocols. Within each framework, multiple components (or “plugins”) can be provided, each with its own implementation of the framework’s abstraction interfaces.

Debugging output in an MCA environment is controlled at the individual framework level using MCA parameters. For example, one can debug the buffer operations (contained in the “bfrops” framework) by setting the PMIX_MCA_bfrops_base_verbose parameter. Parameters can be set in a system-level default file (located in the installation directory as etc/pmix-mca-params.conf), a user-level default file ($HOME/.pmix/mca-params.conf), or on the command line of a supporting tool (e.g., as “-pmca bfrops_base_verbose 5” on the PMIx Reference Server’s “prun” command line).

Beginning with the upcoming v2.1 release, the “pinfo” tool can be used to report the available parameters, their current value, and where they were set. IMPORTANT NOTE: there is a “pinfo” executable in the standard Linux distribution. Please ensure that you have the PMIx install-prefix/bin location at the front of your $PATH environmental variable, or specify the absolute path to the PMIx “pinfo” command.

Unfortunately, this tool is not available in the PMIx v2.0 release series. In this case, one can only refer to the source code itself – each framework is defined as its own subdirectory in the src/mca directory. Of these, the ones of primary interest to users would be the “ptl” (client-server communications), “psec” (security handshake for establishing client-server connections), and “psensor” (local monitors for detecting stalled applications).

Debugging non-plugin code remains under the control of PMIX_DEBUG.

Debugging PMIx Master (v3.x) The PMIx master (currently scheduled for release as v3.x) offers an expanded granularity for debugging output by further splitting the PMIX_DEBUG option to introduce function-specific parameters for both the client and server non-plugin code. Controls include:

There remain a very few places where PMIX_DEBUG is used. We are actively working to eliminate those, but some additional output may be available via that parameter in the interim.