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Subject: Re: [OMPI users] Hybrid OpenMPI / OpenMP run pins OpenMP threads to a single core
From: David Akin (nospamou_at_[hidden])
Date: 2010-07-28 23:40:48


Here's the exact command I'm running when all threads *are* pinned to
a single core:

/usr/mpi/gcc/openmpi-1.4-qlc/bin/mpirun -host c005,c006 -np 2
OMP_NUM_THREADS=4 hybrid4.gcc

Can anyone verify they have the same issue?

On Wed, Jul 28, 2010 at 7:52 PM, Ralph Castain <rhc_at_[hidden]> wrote:
> How are you running it when the threads are all on one core?
>
> If you are specifying --bind-to-core, then of course all the threads will be on one core since we bind the process (not the thread). If you are specifying -mca mpi_paffinity_alone 1, then the same behavior results.
>
> Generally, if you want to bind threads, the only way to do it is with a rank file. We -might- figure out a way to provide an interface for thread-level binding, but I'm not sure about that right now. As things stand, OMPI has no visibility into the fact that your app spawned threads.
>
>
> On Jul 28, 2010, at 5:47 PM, David Akin wrote:
>
>> All,
>> I'm trying to get the OpenMP portion of the code below to run
>> multicore on a couple of 8 core nodes.
>>
>> Good news: multiple threads are being spawned on each node in the run.
>> Bad news: each of the threads only runs on a single core, leaving 7
>> cores basically idle.
>> Sorta good news: if I provide a rank file I get the threads running on
>> different cores within each node (PITA.
>>
>> Here's the first lines of output.
>>
>> /usr/mpi/gcc/openmpi-1.4-qlc/bin/mpirun -host c005,c006 -np 2 -rf
>> rank.file -x OMP_NUM_THREADS=4 hybrid4.gcc
>>
>> Hello from thread 2 out of 4 from process 1 out of 2 on c006.local
>> another parallel region:       name:c006.local MPI_RANK_ID=1 OMP_THREAD_ID=2
>> Hello from thread 3 out of 4 from process 1 out of 2 on c006.local
>> another parallel region:       name:c006.local MPI_RANK_ID=1 OMP_THREAD_ID=3
>> Hello from thread 1 out of 4 from process 1 out of 2 on c006.local
>> another parallel region:       name:c006.local MPI_RANK_ID=1 OMP_THREAD_ID=1
>> Hello from thread 1 out of 4 from process 0 out of 2 on c005.local
>> another parallel region:       name:c005.local MPI_RANK_ID=0 OMP_THREAD_ID=1
>> Hello from thread 3 out of 4 from process 0 out of 2 on c005.local
>> Hello from thread 2 out of 4 from process 0 out of 2 on c005.local
>> another parallel region:       name:c005.local MPI_RANK_ID=0 OMP_THREAD_ID=3
>> another parallel region:       name:c005.local MPI_RANK_ID=0 OMP_THREAD_ID=2
>> Hello from thread 0 out of 4 from process 0 out of 2 on c005.local
>> another parallel region:       name:c005.local MPI_RANK_ID=0 OMP_THREAD_ID=0
>> Hello from thread 0 out of 4 from process 1 out of 2 on c006.local
>> another parallel region:       name:c006.local MPI_RANK_ID=1 OMP_THREAD_ID=0
>> another parallel region:       name:c005.local MPI_RANK_ID=0 OMP_THREAD_ID=3
>> another parallel region:       name:c005.local MPI_RANK_ID=0 OMP_THREAD_ID=2
>> another parallel region:       name:c005.local MPI_RANK_ID=0 OMP_THREAD_ID=0
>> another parallel region:       name:c006.local MPI_RANK_ID=1 OMP_THREAD_ID=3
>> another parallel region:       name:c005.local MPI_RANK_ID=0 OMP_THREAD_ID=3
>> another parallel region:       name:c005.local MPI_RANK_ID=0 OMP_THREAD_ID=2
>> another parallel region:       name:c006.local MPI_RANK_ID=1 OMP_THREAD_ID=0
>> another parallel region:       name:c006.local MPI_RANK_ID=1 OMP_THREAD_ID=1
>> .
>> .
>> .
>>
>> Here's the simple code:
>> #include <stdio.h>
>> #include "mpi.h"
>> #include <omp.h>
>>
>> int main(int argc, char *argv[]) {
>>  int numprocs, rank, namelen;
>>  char processor_name[MPI_MAX_PROCESSOR_NAME];
>>  int iam = 0, np = 1;
>>  char name[MPI_MAX_PROCESSOR_NAME];   /* MPI_MAX_PROCESSOR_NAME ==
>> 128         */
>>  int O_ID;                            /* OpenMP thread ID
>>         */
>>  int M_ID;                            /* MPI rank ID
>>         */
>>  int rtn_val;
>>
>>  MPI_Init(&argc, &argv);
>>  MPI_Comm_size(MPI_COMM_WORLD, &numprocs);
>>  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
>>  MPI_Get_processor_name(processor_name, &namelen);
>>
>>  #pragma omp parallel default(shared) private(iam, np,O_ID)
>>  {
>>    np = omp_get_num_threads();
>>    iam = omp_get_thread_num();
>>    printf("Hello from thread %d out of %d from process %d out of %d on %s\n",
>>           iam, np, rank, numprocs, processor_name);
>>    int i=0;
>>    int j=0;
>>    double counter=0;
>>    for(i =0;i<99999999;i++)
>>            {
>>             O_ID = omp_get_thread_num();          /* get OpenMP
>> thread ID                 */
>>             MPI_Get_processor_name(name,&namelen);
>>             rtn_val = MPI_Comm_rank(MPI_COMM_WORLD,&M_ID);
>>             printf("another parallel region:       name:%s
>> MPI_RANK_ID=%d OMP_THREAD_ID=%d\n", name,M_ID,O_ID);
>>             for(j = 0;j<999999999;j++)
>>              {
>>               counter=counter+i;
>>              }
>>            }
>>
>>  }
>>
>>  MPI_Finalize();
>>
>> }
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