1. Message Queue Dumping MPI Side Document

2. History MPIR and MQD were designed around 1995 MPIR: Process discovery Formally described in the MPIR document in 2010 MQD details were omitted MQD: Message Queue Dumping Many MPI implementations support it and almost all debuggers use it Not yet documented

3. The MQD document V1.0: Documenting existing interface and practice Vnext: Merge with the MPIR document to be one side document Introduce handle introspection interface Other improvements

4. Message Queue Dumping Interface Tools and Debuggers use MQD to extract information about messages Practically, only debuggers (need symbols) Typically there are three conceptual queues: Unexpected Receive Posted Receive Send The MQD allows the following Querying if MQD is supported If yes, allows for iterating over active communicators. Within each communicator, allows for iterating over each message

5. Terms and Definitions DLL: An overloaded term that refers to either: dynamic-link library, dynamically loaded library, dynamic shared object file Image file: An executable or a shared library May contain symbols necessary for MQD MPI Process: An OS process that is part of the MPI application. MPI standard does not require OS process. It’s debuggers’ requirement. mqs_image: abtract concepts that represents collection of image files Loaded into the process address space Can change/relocate during runtime Host: Where we run the debuggers Target: Where the MPI process resides

6. MQD DLL Provided by the MPI implementation Debugger does not need to know the internal implementation Dynamically loaded by the debugger Found by: value of MPIR_dll_name symbol in the process Invoke debugger’s provided functionalities through tables of callbacks Debugger calls routine from the MQD DLL during setup to provide cb’s This allows the debug DLL to work with any MQD-complaint debugger

7. Debugger/Debug DLL interaction See document

8. What’s next Can’t just put MQD at the end of MPIR – Need to merge them in a way that makes sense Handle introspection interface MPIR_dll_name is not sufficient 64-bit MPI process has compiled with MPIR_dll_name pointing to 64-bit debug DLL. 32-bit debugger needs to load 32-bit DLL! Resource management for MPIR How to know if we’re launched under srun, apprun, mpirun. What is the job number, etc. Connectivity information (what are the state of the connection between MPI processes)