Yeah, there was a bug in the code. Fixed now. Brian
On 7/6/12 10:47 AM, "Richard Graham" <richa...@mellanox.com> wrote: >Forget what I just posted - I looked at George's words, and not the code >- wait() is the synchronization point, so George's response is correct. > >Rich > >-----Original Message----- >From: devel-boun...@open-mpi.org [mailto:devel-boun...@open-mpi.org] On >Behalf Of George Bosilca >Sent: Friday, July 06, 2012 2:48 AM >To: eugene....@oracle.com; Open MPI Developers >Cc: Open MPI Developers >Subject: Re: [OMPI devel] non-blocking barrier > >No, it is not right. With the ibarrier usage you're making below, the >output should be similar to the first case (all should leave at earlist >at 6.0). The ibarrier is still a synchronizing point, all processes MUST >reach it before anyone is allowed to leave. > >However, if you move the ibarrier on proc < 2 before the sleep, the >output you got become possible. > > George > > > >On Jul 6, 2012, at 7:53, Eugene Loh <eugene....@oracle.com> wrote: > >> Either there is a problem with MPI_Ibarrier or I don't understand the >>semantics. >> >> The following example is with openmpi-1.9a1r26747. (Thanks for the fix >>in 26757. I tried with that as well with same results.) I get similar >>results for different OSes, compilers, bitness, etc. >> >> % cat ibarrier.c >> #include <stdio.h> >> #include <unistd.h> >> #include <stdlib.h> >> #include <mpi.h> >> >> int main(int argc, char** argv) { >> int i, me; >> double t0, t1, t2; >> MPI_Request req; >> >> MPI_Init(&argc,&argv); >> MPI_Comm_rank(MPI_COMM_WORLD,&me); >> >> MPI_Barrier(MPI_COMM_WORLD); >> MPI_Barrier(MPI_COMM_WORLD); >> MPI_Barrier(MPI_COMM_WORLD); >> t0 = MPI_Wtime(); /* set "time zero" */ >> >> if ( me < 2 ) sleep(3); /* two processes delay before hitting >>barrier */ >> t1 = MPI_Wtime() - t0; >> MPI_Barrier(MPI_COMM_WORLD); >> t2 = MPI_Wtime() - t0; >> printf("%d entered at %3.1lf and exited at %3.1lf\n", me, t1, t2); >> >> if ( me < 2 ) sleep(3); /* two processes delay before hitting >>barrier */ >> t1 = MPI_Wtime() - t0; >> MPI_Ibarrier(MPI_COMM_WORLD, &req); >> MPI_Wait(&req, MPI_STATUS_IGNORE); >> t2 = MPI_Wtime() - t0; >> printf("%d entered at %3.1lf and exited at %3.1lf\n", me, t1, t2); >> >> MPI_Finalize(); >> return 0; >> } >> % mpirun -n 4 ./a.out >> 0 entered at 3.0 and exited at 3.0 >> 1 entered at 3.0 and exited at 3.0 >> 2 entered at 0.0 and exited at 3.0 >> 3 entered at 0.0 and exited at 3.0 >> 0 entered at 6.0 and exited at 6.0 >> 1 entered at 6.0 and exited at 6.0 >> 2 entered at 3.0 and exited at 3.0 >> 3 entered at 3.0 and exited at 3.0 >> >> With the first barrier, no one leaves until the last process has >>entered. With the non-blocking barrier, two processes enter and leave >>before the two laggards arrive at the barrier. Is that right? >> _______________________________________________ >> devel mailing list >> de...@open-mpi.org >> http://www.open-mpi.org/mailman/listinfo.cgi/devel > >_______________________________________________ >devel mailing list >de...@open-mpi.org >http://www.open-mpi.org/mailman/listinfo.cgi/devel > >_______________________________________________ >devel mailing list >de...@open-mpi.org >http://www.open-mpi.org/mailman/listinfo.cgi/devel > >
