Hi,
I am running some tests on Amazon EC2 and they require a lot of
communication among m3.large instances.
I would like to give you an idea of what kind of communication takes place.
There are 40 m3.large instances. Now, 28672 groups of 5 instances are
formed in a specific manner (let's skip the details). Within each group,
each instance broadcasts some unsigned char data to the other 4 instances
in the group. So within each group, exactly 5 broadcasts take place.
The problem is that if I increase the size of the group from 5 to 10 there
is significant delay in terms of transmission rate while, based on some
theoretical results, this is not reasonable.
I want to check if one of the reasons that this is happening is due to the
time needed for the instances to synchronize when they call MPI_Bcast()
since it's a collective function. As far as I know, all of the machines in
the broadcast need to call it and then synchronize until the actual data
transfer starts. Is there any way to measure this synchronization time?
The code is in C++ and the MPI installed is described in the attached file.
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
MCA backtrace: execinfo (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA compress: gzip (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA compress: bzip (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA crs: none (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA db: print (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA db: hash (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA dl: dlopen (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA event: libevent2021 (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA hwloc: external (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA if: posix_ipv4 (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA if: linux_ipv6 (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA installdirs: env (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA installdirs: config (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA memory: linux (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA pstat: linux (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA sec: basic (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA shmem: posix (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA shmem: sysv (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA shmem: mmap (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA timer: linux (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA dfs: test (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA dfs: app (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA dfs: orted (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA errmgr: default_hnp (MCA v2.0.0, API v3.0.0, Component
v1.10.2)
MCA errmgr: default_orted (MCA v2.0.0, API v3.0.0, Component
v1.10.2)
MCA errmgr: default_tool (MCA v2.0.0, API v3.0.0, Component
v1.10.2)
MCA errmgr: default_app (MCA v2.0.0, API v3.0.0, Component
v1.10.2)
MCA ess: slurm (MCA v2.0.0, API v3.0.0, Component v1.10.2)
MCA ess: env (MCA v2.0.0, API v3.0.0, Component v1.10.2)
MCA ess: singleton (MCA v2.0.0, API v3.0.0, Component
v1.10.2)
MCA ess: tool (MCA v2.0.0, API v3.0.0, Component v1.10.2)
MCA ess: hnp (MCA v2.0.0, API v3.0.0, Component v1.10.2)
MCA filem: raw (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA grpcomm: bad (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA iof: tool (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA iof: mr_orted (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA iof: orted (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA iof: mr_hnp (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA iof: hnp (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA odls: default (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA oob: tcp (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA plm: slurm (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA plm: rsh (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA plm: isolated (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA ras: slurm (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA ras: simulator (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA ras: loadleveler (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA ras: gridengine (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA rmaps: rank_file (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA rmaps: seq (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA rmaps: mindist (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA rmaps: staged (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA rmaps: ppr (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA rmaps: resilient (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA rmaps: round_robin (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA rml: oob (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA routed: binomial (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA routed: radix (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA routed: debruijn (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA routed: direct (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA state: staged_orted (MCA v2.0.0, API v1.0.0, Component
v1.10.2)
MCA state: hnp (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA state: staged_hnp (MCA v2.0.0, API v1.0.0, Component
v1.10.2)
MCA state: orted (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA state: app (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA state: dvm (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA state: tool (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA state: novm (MCA v2.0.0, API v1.0.0, Component v1.10.2)
MCA allocator: basic (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA allocator: bucket (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA bcol: basesmuma (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA bcol: ptpcoll (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA bml: r2 (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA btl: self (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA btl: tcp (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA btl: openib (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA btl: sm (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA btl: vader (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA coll: self (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA coll: sm (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA coll: libnbc (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA coll: tuned (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA coll: hierarch (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA coll: basic (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA coll: inter (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA coll: ml (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA dpm: orte (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA fbtl: posix (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA fcoll: dynamic (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA fcoll: two_phase (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA fcoll: ylib (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA fcoll: static (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA fcoll: individual (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA fs: ufs (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA io: romio (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA io: ompio (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA mpool: grdma (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA mpool: sm (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA osc: sm (MCA v2.0.0, API v3.0.0, Component v1.10.2)
MCA osc: pt2pt (MCA v2.0.0, API v3.0.0, Component v1.10.2)
MCA pml: v (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA pml: cm (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA pml: bfo (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA pml: ob1 (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA pubsub: orte (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA rcache: vma (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA rte: orte (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA sbgp: basesmsocket (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA sbgp: basesmuma (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA sbgp: p2p (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA sharedfp: lockedfile (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA sharedfp: individual (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
MCA sharedfp: sm (MCA v2.0.0, API v2.0.0, Component v1.10.2)
MCA topo: basic (MCA v2.0.0, API v2.1.0, Component v1.10.2)
MCA vprotocol: pessimist (MCA v2.0.0, API v2.0.0, Component
v1.10.2)
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