Assume that we have K=q*k nodes (slaves) where q,k are positive integers >=
2.
Based on the scheme that I am currently using I create [q^(k-1)]*(q-1)
groups (along with their communicators). Each group consists of k nodes and
within each group exactly k broadcasts take place (each node broadcasts
something to the rest of them). So in total [q^(k-1)]*(q-1)*k MPI
broadcasts take place. Let me skip the details of the above scheme.
Now theoretically I figured out that there are q-1 groups that can
communicate in parallel at the same time i.e. groups that have no common
nodes and I would like to utilize that to speedup the shuffling. I have
seen here
https://stackoverflow.com/questions/11372012/mpi-several-broadcast-at-the-same-time
that
this is possible in MPI.
In my case it's more complicated since q,k are parameters of the problem
and change between different experiments. If I get the idea about the 2nd
method that is proposed there and assume that we have only 3 groups within
which some communication takes places one can simply do:
*if my rank belongs to group 1{*
* comm1.Bcast(..., ..., ..., rootId);*
*}else if my rank belongs to group 2{*
* comm2.Bcast(..., ..., ..., rootId);*
*}else if my rank belongs to group3{*
* comm3.Bcast(..., ..., ..., rootId);*
*} *
where comm1, comm2, comm3 are the corresponding sub-communicators that
contain only the members of each group.
But how can I generalize the above idea to arbitrary number of groups or
perhaps do something else?
The code is in C++ and the MPI installed is described in the attached file.
Regards,
Kostas
Package: Open MPI buildd@lgw01-57 Distribution
Open MPI: 1.10.2
Open MPI repo revision: v1.10.1-145-g799148f
Open MPI release date: Jan 21, 2016
Open RTE: 1.10.2
Open RTE repo revision: v1.10.1-145-g799148f
Open RTE release date: Jan 21, 2016
OPAL: 1.10.2
OPAL repo revision: v1.10.1-145-g799148f
OPAL release date: Jan 21, 2016
MPI API: 3.0.0
Ident string: 1.10.2
Prefix: /usr
Configured architecture: x86_64-pc-linux-gnu
Configure host: lgw01-57
Configured by: buildd
Configured on: Thu Feb 25 16:33:01 UTC 2016
Configure host: lgw01-57
Built by: buildd
Built on: Thu Feb 25 16:40:59 UTC 2016
Built host: lgw01-57
C bindings: yes
C++ bindings: yes
Fort mpif.h: yes (all)
Fort use mpi: yes (full: ignore TKR)
Fort use mpi size: deprecated-ompi-info-value
Fort use mpi_f08: yes
Fort mpi_f08 compliance: The mpi_f08 module is available, but due to
limitations in the gfortran compiler, does not
support the following: array subsections, direct
passthru (where possible) to underlying Open MPI's
C functionality
Fort mpi_f08 subarrays: no
Java bindings: no
Wrapper compiler rpath: runpath
C compiler: gcc
C compiler absolute: /usr/bin/gcc
C compiler family name: GNU
C compiler version: 5.3.1
C++ compiler: g++
C++ compiler absolute: /usr/bin/g++
Fort compiler: gfortran
Fort compiler abs: /usr/bin/gfortran
Fort ignore TKR: yes (!GCC$ ATTRIBUTES NO_ARG_CHECK ::)
Fort 08 assumed shape: yes
Fort optional args: yes
Fort INTERFACE: yes
Fort ISO_FORTRAN_ENV: yes
Fort STORAGE_SIZE: yes
Fort BIND(C) (all): yes
Fort ISO_C_BINDING: yes
Fort SUBROUTINE BIND(C): yes
Fort TYPE,BIND(C): yes
Fort T,BIND(C,name="a"): yes
Fort PRIVATE: yes
Fort PROTECTED: yes
Fort ABSTRACT: yes
Fort ASYNCHRONOUS: yes
Fort PROCEDURE: yes
Fort USE...ONLY: yes
Fort C_FUNLOC: yes
Fort f08 using wrappers: yes
Fort MPI_SIZEOF: yes
C profiling: yes
C++ profiling: yes
Fort mpif.h profiling: yes
Fort use mpi profiling: yes
Fort use mpi_f08 prof: yes
C++ exceptions: no
Thread support: posix (MPI_THREAD_MULTIPLE: no, OPAL support: yes,
OMPI progress: no, ORTE progress: yes, Event lib:
yes)
Sparse Groups: no
Internal debug support: no
MPI interface warnings: yes
MPI parameter check: runtime
Memory profiling support: no
Memory debugging support: no
dl support: yes
Heterogeneous support: yes
mpirun default --prefix: no
MPI I/O support: yes
MPI_WTIME support: gettimeofday
Symbol vis. support: yes
Host topology support: yes
MPI extensions:
FT Checkpoint support: no (checkpoint thread: no)
C/R Enabled Debugging: no
VampirTrace support: no
MPI_MAX_PROCESSOR_NAME: 256
MPI_MAX_ERROR_STRING: 256
MPI_MAX_OBJECT_NAME: 64
MPI_MAX_INFO_KEY: 36
MPI_MAX_INFO_VAL: 256
MPI_MAX_PORT_NAME: 1024
MPI_MAX_DATAREP_STRING: 128
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MCA vprotocol: pessimist (MCA v2.0.0, API v2.0.0, Component
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