[mpich-discuss] intercommunicator support in MPICH

[Rajeev Thakur]

Intercommunicators as defined in MPI-1 with a static set of processes
should work everywhere. MPI-2 dynamic process management functions
(spawn, connect/accept), which also use intercommunicators, are not
supported by IBM and Cray MPIs as far as I know.

Rajeev
 

> -----Original Message-----
> From: mpich-discuss-bounces at mcs.anl.gov 
> [mailto:mpich-discuss-bounces at mcs.anl.gov] On Behalf Of Rob Latham
> Sent: Tuesday, July 20, 2010 8:06 AM
> To: mpich-discuss at mcs.anl.gov
> Subject: [mpich-discuss] intercommunicator support in MPICH
> 
> Hi Jim.  I'm interested in hearing more about how this async 
> i/o strategy plays out on other platforms.  
> 
> I'm moving this to the mpich-discuss list, because as far as 
> I know intercommunicators are supported on MPICH2, but the 
> folks on the mpich-discuss list will be able to speak with 
> more authority on that matter.
> 
> What is it about intercommunicators that does not work for you?  Are
> you splitting up COMM_WORLD to form comp_comm and io_comm ?   
> 
> There might be performance implications with 
> intercommunicators.  Can the link between the two sets be the 
> bottleneck here?  I presume  you are transferring a lot of 
> data to io_comm.  
> 
> MPICH guys, Jim's original email is below. 
> ==rob
> 
> On Mon, Jul 19, 2010 at 04:44:50PM -0600, Jim Edwards wrote:
> > Hi All,
> > 
> > I have created a new repository branch and checked in the 
> beginnings 
> > of a version of pio which allows the io tasks to be a 
> disjoint set of 
> > tasks from those used for computation.
> > 
> > The io_comm and the comp_comm are disjoint and pio_init
> > is called with an intercommunicator which spans the two 
> task sets.   The
> > compute task set returns while the io task set waits in a call back 
> > loop for further instructions.
> > 
> > I have added three new tests in the pio test suite and all 
> of them pass on
> > bluefire.   Then I discovered that the mpich  does not support mpi
> > intercommunicators.    These are part of the mpi-2 standard 
> and I thought
> > that all of the mpi implementations were there by now?  
> Apparently not.   Is
> > there another mpi implementation that we can try on jaguar 
> or edinburgh?
> > 
> > Currently all of the pio commands are still syncronous 
> calls - that is 
> > the compute tasks cannot continue until the write has completed, my 
> > eventual plan is to relax this requirement to see if there is a 
> > performance advantage
> > - but if AIX-POE is the only environment to support this 
> model I may 
> > have to rethink the approach.
> > 
> > If you get a chance please have a look at the implementation in 
> > https://parallelio.googlecode.com/svn/branches/async_pio1_1_1/
> > 
> > If enough of you are interested we can schedule a con-call 
> to go over 
> > how it works and some of the things that still need to be done.
> > 
> > Jim
> > 
> 
> --
> Rob Latham
> Mathematics and Computer Science Division Argonne National 
> Lab, IL USA _______________________________________________
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