What: A Runtime Interposition Project - Codename Pineapple Why: Define clear API and semantics for runtime requirements of the OMPI layer.
When: - F June 22, 2012 - Work completed - T June 26, 2012 - Discuss on teleconf - R June 28, 2012 - Commit to trunk Where: Trunk (development BitBucket branch below) https://bitbucket.org/jjhursey/ompi-pineapple Attached: PDF of slides presented on the June 12, 2012 teleconf. Note that the timeline was slightly adjusted above (work completed date moved ealier). Description: Short Version -------------------------- Define, in an 'rte.h', the interfaces and semantics that the OMPI layer requires of a runtime environment. Currently this interface matches the subset of ORTE functionality that is used by the OMPI layer. Runtime symbols (e.g., orte_ess.proc_get_locality) are isolated to a framework inside this project to provide linker-level protection against accidental breakage of the pineapple interposition layer. The interposition project provides researchers working on side projects above and below the 'rte.h' interface a single location in the code base to watch for interface and semantic changes that they need to be concerned about. Researchers working above the pineapple layer might explore something other than (or in addition to) OMPI (e.g., Extended OMPI, UPC+OMPI). Researchers working below the pineapple layer might explore something other than (or in addition to) ORTE under OMPI (e.g., specialized runtimes for specific environments). Description: Other notes ------------------------ The pineapple interface provides OMPI developers with a runtime API to program against without requiring detailed knowledge of the layout of ORTE and its frameworks. In some places in OMPI a single source file needs to include >5 (up to 12 in one place) different header files to get all of the necessary symbols. Developers must not only know where these headers are, but must also understand the differences between the various frameworks in ORTE to use ORTE. The developer must also be aware that there are certain APIs and data structure fields that are not available to the MPI process, so should not be used. The pineapple project provides an API representing the small subset of ORTE that is used by OMPI. With this API a developer only needs to look at a single location in the code base to understand what is provided by the runtime for use in the OMPI layer. A similar statement could be made for runtime developers trying to figure out what the OMPI layer requires from the a runtime environment. Currently they need a deep understanding of the behavior of ORTE to understand the semantics of various calls to ORTE from the OMPI layer. Then they must develop a custom patch for the OMPI layer that extracts the ORTE symbols, and replaces them with their own symbols. This process is messy, error prone, and tedious to say the least. Having a single set of interfaces and semantics will allow such developers to focus their efforts on supporting the Open MPI community defined API, and not necessarily the evolution of the ORTE or OMPI project internals. This is advantageous when porting Open MPI to an environment with a full featured runtime already running on the machine, and for researchers exploring radical runtime designs for future systems. The pineapple API allows such projects to develop beside the mainline Open MPI trunk a little more easily than without the pineapple API. FAQ: ---- (1) Why is this a separate project and not a framework of OMPI? or a framework of ORTE? After much deliberation between the developers, from a software engineering perspective, making the pineapple rte.h interface a separate project was the most flexible solution. So neither the OMPI layer nor the ORTE layer 'own' the interface, but it is 'owned' by the Open MPI project primarily to support the interaction between these two layers. Consider that if we decided to place the interface in the OMPI layer as a framework then we would be able to place something other than (or in addition to) ORTE underneath OMPI, but we would be limited in our ability to place something other than (or in addition to) OMPI over ORTE. Alternatively, if we decided to place the rte.h interface in the ORTE layer then we would be able to place something other than (or in addition to) OMPI over ORTE, but we would be limited in our ability to place something other than (or in addition to) ORTE under OMPI. Defining the interposition layer as a separate project between these two layers allows maximal flexibility for the project and researchers working on side branches. (2) What if another project outside of Open MPI needs interface changes to the pineapple 'rte.h'? The rule of thumb is that 'The OMPI/ORTE/OPAL stack is king!'. This means that the pineapple project should always err on the side of supporting the OMPI/ORTE/OPAL stack, as that is the flagship product of the Open MPI project. Interface suggestions are always welcome and the rte.h may be extended/modified in the future as a result of those suggestions. However, if a suggested change negatively impacts the OMPI/ORTE/OPAL stack then it is unlikely to be accepted upstream by the Open MPI community. -- Joshua Hursey Postdoctoral Research Associate Oak Ridge National Laboratory http://users.nccs.gov/~jjhursey
Pineapple-Teleconf.pdf
Description: Adobe PDF document
