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Subject: Re: [OMPI users] Hybrid OpenMPI / OpenMP run pins OpenMP threads to a single core
From: Ralph Castain (rhc_at_[hidden])
Date: 2010-07-29 09:49:24


On Jul 29, 2010, at 5:09 AM, Terry Dontje wrote:

> Ralph Castain 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.
>>
>>
>>
> Huh??? That's not completely correct. If you have a multiple socket machine you could to -bind-to-socket -bysocket and spread the processes that way. Also couldn't you use the -cpus-per-proc with -bind-to-core to get a process to bind to a non-socket amount of cpus?

Yes, you could do bind-to-socket, though that still constrains the threads to only that one socket. What was asked about here was the ability to bind-to-core at the thread level, and that is something OMPI doesn't support.

>
> This is all documented in the mpirun manpage.
>
> That being said, I also am confused, like Ralph, as to why no options is causing your code bind. Maybe add a --report-bindings to your mpirun line to see what OMPI thinks it is doing in this regard?

This is a good suggestion - I'm beginning to believe that the binding is happening in the user's app and not OMPI.

>
> --td
>
> --td
>> 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();
>>>
>>> }
>>> _______________________________________________
>>> users mailing list
>>> users_at_[hidden]
>>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>>
>>
>>
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>
>
> --
> <Mail Attachment.gif>
> Terry D. Dontje | Principal Software Engineer
> Developer Tools Engineering | +1.650.633.7054
> Oracle - Performance Technologies
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> Email terry.dontje_at_[hidden]
>
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