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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: 2010-07-29 13:24:40


I use the taskset command, or just use 'top' and watch the performance.

On Thu, Jul 29, 2010 at 12:02 PM, Ralph Castain <rhc_at_[hidden]> wrote:

> I don't see anything in your code that would bind, but I also don't see
> anything that actually tells you whether or not your are bound. It appears
> that MPI_Get_processor_name is simply returning the name of the node as
> opposed to the name/id of any specific core. How do you know what core the
> thread is actually executing on?
>
>
>
> This would tell you if your code was bouncing between cores.
>
> On Jul 29, 2010, at 10:43 AM, David Akin wrote:
>
> Sorry for the confusion. What I need is for all OpenMP threads to *not*
> stay on one core. I *would* rather each OpenMP thread to run on a separate
> core. Is it my example code? My gut reaction is no because I can manipulate
> (somewhat) the cores the threads are assigned by adding -bysocket
> -bind-to-socket to mpirun.
>
> On Thu, Jul 29, 2010 at 10:08 AM, Terry Dontje <terry.dontje_at_[hidden]>wrote:
>
>> 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();
>>
>> }
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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]
>>
>> _______________________________________________
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>>
>>
>> ------------------------------
>>
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>>
>>
>>
>> --
>> [image: 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]
>>
>>
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>
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-- 
David Akin, RHCE
Sr. Systems Analyst and HPC Roadie
OU Supercomputing Center for Education & Research (OSCER)
University of Oklahoma Information Technology
david.akin_at_[hidden]
405-598-7685
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