#1884: provide support for multi-model runs in thorn MPI -----------------------------------+---------------------------------------- Reporter: rhaas | Owner: Type: enhancement | Status: new Priority: minor | Milestone: Component: EinsteinToolkit thorn | Version: development version Keywords: MPI | -----------------------------------+---------------------------------------- The attached patch adds a very thin layer of code to ExternalLibraries/MPI to provide access to two communicators {{{MPI_Comm_World}}} and {{{MPI_Comm_Universe}}} which can be used for multi-model runs (or runs started via {{{MPI_Comm_Spawn}}}).
The code does not itself split a communicator, it only provides routines to get and set the communicators.
It supports C and F90 calls (and C++ calls through external C and call from F77 files since Cactus compiles those with at a F90 compiler).
Documentation is provided in the tex file and in the grdoc comments.
#1884: provide support for multi-model runs in thorn MPI ------------------------------------+--------------------------------------- Reporter: rhaas | Owner: Type: enhancement | Status: review Priority: minor | Milestone: Component: EinsteinToolkit thorn | Version: development version Resolution: | Keywords: MPI ------------------------------------+--------------------------------------- Changes (by rhaas):
* status: new => review
#1884: provide support for multi-model runs in thorn MPI ------------------------------------+--------------------------------------- Reporter: rhaas | Owner: Type: enhancement | Status: review Priority: minor | Milestone: Component: EinsteinToolkit thorn | Version: development version Resolution: | Keywords: MPI ------------------------------------+---------------------------------------
Comment (by eschnett):
Carpet currently provides aliased functions for this. Presumably, all drivers that support multi-model runs could provide such an aliased function. What is the advantage of an explicit function definition in thorn MPI?
#1884: provide support for multi-model runs in thorn MPI ------------------------------------+--------------------------------------- Reporter: rhaas | Owner: Type: enhancement | Status: review Priority: minor | Milestone: Component: EinsteinToolkit thorn | Version: development version Resolution: | Keywords: MPI ------------------------------------+---------------------------------------
Comment (by rhaas):
I am no longer sure.
For C, the functionality is the identical between this and Carpet I think. The code would only collect the functionality on one spot rather than in each driver.
I think for Fortran, however, Carpet's aliased functions won't work since there is no way to dereference the returned CCTK_POINTER_TO_CONST. The returned pointer is a pointer to the C MPI communicator struct, which (as far as I know) does not have to be bit-identical to Fortran's MPI_Communicator type (which is INT).
Having said all of this, the original usage case I had for this no longer exists (I think it had to do with running PUGH under LoadLeveler or something similar, I have PUGH/Carpet patches that would make user of this code to provide the aliased functions). The implementation of the Reset functions is also somewhat ugly.
#1884: provide support for multi-model runs in thorn MPI ------------------------------------+--------------------------------------- Reporter: rhaas | Owner: Type: enhancement | Status: closed Priority: minor | Milestone: Component: EinsteinToolkit thorn | Version: development version Resolution: wontfix | Keywords: MPI ------------------------------------+--------------------------------------- Changes (by rhaas):
* status: review => closed * resolution: => wontfix
Comment:
Come to think of it, unless there is need for it, I'd keep the complex code out the ET.
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