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Subject: Re: [OMPI users] Hybrid OpenMPI / OpenMP run pins OpenMP threads to a single core
From: Terry Dontje (terry.dontje_at_[hidden])
Date: 2010-07-29 11:08:35


Ralph Castain wrote:
>
> 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.
>
Sorry I did not get that constraint. So to be clear what is being asked
is to have the ability to bind a processes threads to specific cores.
If so then to the letter of what that means I agree you cannot do that.

However, what may be the next best thing is to specify binding of a
process to a group of resources. That's essentially what my suggestion
above is doing.

I do agree with Ralph that once you start overloading the socket with
more threads then it can handle problems will ensue.

--td
>
>>
>> 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*
>> 95 Network Drive, Burlington, MA 01803
>> Email terry.dontje_at_[hidden] <mailto:terry.dontje_at_[hidden]>
>>
>> _______________________________________________
>> users mailing list
>> users_at_[hidden] <mailto:users_at_[hidden]>
>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
> ------------------------------------------------------------------------
>
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-- 
Oracle
Terry D. Dontje | Principal Software Engineer
Developer Tools Engineering | +1.650.633.7054
Oracle * - Performance Technologies*
95 Network Drive, Burlington, MA 01803
Email terry.dontje_at_[hidden] <mailto:terry.dontje_at_[hidden]>



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