Hi!
It is in so far related, that one of these threads is actually doing
something.
Btw, I noticed this on two separate machines! A computing cluster with
admin-built openmpi and Archlinux with openmpi from the repositories.
However, running the code with openmpi 1.6.2 and ifort 13.0.0 does not
show this behaviour.
Best regards,
Stefan
On 01/07/2016 03:27 PM, Sasso, John (GE Power, Non-GE) wrote:
Stefan, I don't know if this is related to your issue, but FYI...
Those are async progress threads - they block unless something requires doing
On Apr 15, 2015, at 8:36 AM, Sasso, John (GE Power & Water, Non-GE)
<john1.sa...@ge.com> wrote:
I stumbled upon something while using 'ps -eFL' to view threads of processes,
and Google searches have failed to answer my question. This question holds for
OpenMPI 1.6.x and even OpenMPI 1.4.x.
>>
For a program which is pure MPI (built and run using OpenMPI) and does not
implement Pthreads or OpenMP, why is it that each MPI task appears as having 3
threads:
>>
UID PID PPID LWP C NLWP SZ RSS PSR STIME TTY TIME CMD
sasso 20512 20493 20512 99 3 187849 582420 14 11:01 ? 00:26:37
/home/sasso/mpi_example.exe
sasso 20512 20493 20588 0 3 187849 582420 11 11:01 ? 00:00:00
/home/sasso/mpi_example.exe
sasso 20512 20493 20599 0 3 187849 582420 12 11:01 ? 00:00:00
/home/sasso/mpi_example.exe
>>
whereas if I compile and run a non-MPI program, 'ps -eFL' shows it running as a
single thread?
Granted the CPU utilization (C) for 2 of the 3 threads is zero, but the threads
are bound to different processors (11,12,14). I am curious as to why this is,
and no complaining that there is a problem. Thanks!
>>
--john
-----Original Message-----
From: users [mailto:users-boun...@open-mpi.org] On Behalf Of Au Eelis
Sent: Thursday, January 07, 2016 7:10 AM
To: us...@open-mpi.org
Subject: [OMPI users] Singleton process spawns additional thread
Hi!
I have a weird problem with executing a singleton OpenMPI program, where an
additional thread causes full load, while the master thread performs the actual
calculations.
In contrast, executing "mpirun -np 1 [executable]" performs the same
calculation at the same speed but the additional thread is idling.
In my understanding, both calculations should behave in the same way (i.e., one
working thread) for a program which is simply moving some data around (mainly
some MPI_BCAST and MPI_GATHER commands).
I could observe this behaviour in OpenMPI 1.10.1 with ifort 16.0.1 and gfortran
5.3.0. I could create a minimal working example, which is appended to this mail.
Am I missing something?
Best regards,
Stefan
-----
MWE: Compile this with "mpifort main.f90". When executing with "./a.out", there is thread
wasting cycles, while the master thread waits for input. When executing with "mpirun -np 1 ./a.out"
this thread is idling.
program main
use mpi_f08
implicit none
integer :: ierror,rank
call MPI_Init(ierror)
call MPI_Comm_Rank(MPI_Comm_World,rank,ierror)
! let master thread wait on [RETURN]-key
if (rank == 0) then
read(*,*)
end if
write(*,*) rank
call mpi_barrier(mpi_comm_world, ierror) end program
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