This looks good. If performance is critical you can speed up the entire process by using MPI_Comm_create_group instead of the second MPI_COMM_SPLIT. The MPI_Comm_create_group is collective only over the resulting communicator and not over the source communicator, so its cost is only dependent of the number of groups and not on the total number of processes.
You can also try to replace the first MPI_COMM_SPLIT by the same approach. I would be curious to see the outcome. George. On Thu, Jul 27, 2017 at 9:44 AM, Diego Avesani <diego.aves...@gmail.com> wrote: > Dear George, Dear all, > > I have tried to create a simple example. In particular, I would like to > use 16 CPUs and to create four groups according to rank is and then a > communicator between masters of each group.I have tried to follow the first > part of this example > <http://mpitutorial.com/tutorials/introduction-to-groups-and-communicators/>. > In the last part I have tried to create a communicator be masters as > suggested by George. > > Here my example: > > CALL MPI_INIT(ierror) > CALL MPI_COMM_SIZE(MPI_COMM_WORLD, nCPU, ierror) > CALL MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierror) > ! > colorloc = rank/4 > ! > CALL MPI_COMM_SPLIT(MPI_COMM_WORLD,colorloc,rank,*NEW_COMM*,ierror) > CALL MPI_COMM_RANK(*NEW_COMM*, subrank,ierror); > CALL MPI_COMM_SIZE(*NEW_COMM*, subnCPU,ierror); > ! > IF(MOD(rank,4).EQ.0)THEN > *! where I set color for the masters* > colorglobal = MOD(rank,4) > ELSE > colorglobal = MPI_UNDEFINED > ENDIF > ! > CALL MPI_COMM_SPLIT(MPI_COMM_WORLD,colorglobal,rank,LEADER_COMM,ierror) > CALL MPI_COMM_RANK(*LEADER_COMM*, leader_rank,ierror); > CALL MPI_FINALIZE(ierror) > > I would like to know if this could be correct. I mean if I have understood > correctly what George told me about the code design. Now, this example does > not work, but probably there is some coding error. > > Really, Really thanks > Diego > > > > > > > > Diego > > > On 27 July 2017 at 10:42, Diego Avesani <diego.aves...@gmail.com> wrote: > >> Dear George, Dear all, >> >> A question regarding program design: >> The draft that I have sent to you has to be done many and many times. >> Does the splitting procedure ensure efficiency? >> >> I will try, at a lest to create groups and split them. I am a beginner in >> the MPI groups environment. >> really, really thanks. >> >> You are my lifesaver. >> >> >> >> Diego >> >> >> On 26 July 2017 at 15:09, George Bosilca <bosi...@icl.utk.edu> wrote: >> >>> Diego, >>> >>> As all your processes are started under the umbrella of a single mpirun, >>> they have a communicator in common, the MPI_COMM_WORLD. >>> >>> One possible implementation, using MPI_Comm_split, will be the following: >>> >>> MPI_Comm small_comm, leader_comm; >>> >>> /* Create small_comm on all processes */ >>> >>> /* Now use MPI_Comm_split on MPI_COMM_WORLD to select the leaders */ >>> MPI_Comm_split( MPI_COMM_WORLD, >>> i_am_leader(small_comm) ? 1 : >>> MPI_UNDEFINED, >>> rank_in_comm_world, >>> &leader_Comm); >>> >>> The leader_comm will be a valid communicator on all leaders processes, >>> and MPI_COMM_NULL on all others. >>> >>> George. >>> >>> >>> >>> On Wed, Jul 26, 2017 at 4:29 AM, Diego Avesani <diego.aves...@gmail.com> >>> wrote: >>> >>>> Dear George, Dear all, >>>> >>>> I use "mpirun -np xx ./a.out" >>>> >>>> I do not know if I have some common grounds. I mean, I have to >>>> design everything from the begging. You can find what I would like to do in >>>> the attachment. Basically, an MPI cast in another MPI. Consequently, I am >>>> thinking to MPI groups or MPI virtual topology with a 2D cart, using the >>>> columns as "groups" and the first rows as the external groups to handle the >>>> columns. >>>> >>>> What do think? What do you suggest? >>>> Really Really thanks >>>> >>>> >>>> Diego >>>> >>>> >>>> On 25 July 2017 at 19:26, George Bosilca <bosi...@icl.utk.edu> wrote: >>>> >>>>> Diego, >>>>> >>>>> Assuming you have some common grounds between the 4 initial groups >>>>> (otherwise you will have to connect them via >>>>> MPI_Comm_connect/MPI_Comm_accept) >>>>> you can merge the 4 groups together and then use any MPI mechanism to >>>>> create a partial group of leaders (such as MPI_Comm_split). >>>>> >>>>> If you spawn the groups via MPI_Comm_spawn then the answer is slightly >>>>> more complicated, you need to use MPI_Intercomm_create, with the spawner >>>>> as >>>>> the bridge between the different communicators (and then >>>>> MPI_Intercomm_merge to create your intracomm). You can find a good answer >>>>> on stackoverflow on this at https://stackoverflow.com/ques >>>>> tions/24806782/mpi-merge-multiple-intercoms-into-a-single-intracomm >>>>> >>>>> How is your MPI environment started (single mpirun or mpi_comm_spawn) ? >>>>> >>>>> George. >>>>> >>>>> >>>>> >>>>> On Tue, Jul 25, 2017 at 10:44 AM, Diego Avesani < >>>>> diego.aves...@gmail.com> wrote: >>>>> >>>>>> Dear All, >>>>>> >>>>>> I am studying Groups and Communicators, but before start going in >>>>>> detail, I have a question about groups. >>>>>> >>>>>> I would like to know if is it possible to create a group of masters >>>>>> of the other groups and then a intra-communication in the new group. I >>>>>> have >>>>>> spent sometime reading different tutorial and presentation, but it is >>>>>> difficult, at least for me, to understand if is it possible to create >>>>>> this >>>>>> sort of MPI cast in another MPI. >>>>>> >>>>>> In the attachment you can find a pictures that summarize what I would >>>>>> like to do. >>>>>> >>>>>> Another strategies could be use virtual topology. >>>>>> >>>>>> What do you think? >>>>>> >>>>>> I really, really, appreciate any kind of help, suggestions or link >>>>>> where I can study this topics. >>>>>> >>>>>> Again, thanks >>>>>> >>>>>> Best Regards, >>>>>> >>>>>> Diego >>>>>> >>>>>> _______________________________________________ >>>>>> users mailing list >>>>>> users@lists.open-mpi.org >>>>>> https://rfd.newmexicoconsortium.org/mailman/listinfo/users >>>>>> >>>>> >>>>> >>>>> _______________________________________________ >>>>> users mailing list >>>>> users@lists.open-mpi.org >>>>> https://rfd.newmexicoconsortium.org/mailman/listinfo/users >>>>> >>>> >>>> >>>> _______________________________________________ >>>> users mailing list >>>> users@lists.open-mpi.org >>>> https://rfd.newmexicoconsortium.org/mailman/listinfo/users >>>> >>> >>> >>> _______________________________________________ >>> users mailing list >>> users@lists.open-mpi.org >>> https://rfd.newmexicoconsortium.org/mailman/listinfo/users >>> >> >> > > _______________________________________________ > users mailing list > users@lists.open-mpi.org > https://rfd.newmexicoconsortium.org/mailman/listinfo/users >
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