[MPICH] Binding and instance of the MPI program to a particular processor

[Javier Vázquez]

Hello,
    
      There is a work about this matters, it tells that a program can 
take benefit from the binding threads to processors depending of its 
granularity, it tells that most programs with fine grained parallelism 
are the best candidate for it.

  *Evaluating the Performance Implications of Binding Threads to Processors.

*Also it tells something related about Christina's situation, specially 
the Solaris with 8 processors.  *

*I hope this help.     

Warm Regards.

        


William Gropp wrote:
> That's a good point.  I'd like to see the reference, because I don't 
> see how the scheduler can be sure that the data in cache won't be 
> needed in the near future (after all, the compiler often can't predict 
> this).  That is, it doesn't matter if the data is out of the cache; 
> for performance on many scientific workloads, it is essential to reuse 
> data that is already in cache, and if the data must be reloaded, 
> performance will plummet.
>
> Bill
>
> On Jun 21, 2007, at 10:49 AM, Diego M. Vadell wrote:
>
>> Hi,
>>     Is there any proof (e.g. benchmark) that binding a process to a
>> processor/core is better than letting the scheduler work things out? I
>> remember reading - sorry for the lack of reference - that linux's 
>> scheduler
>> knows about the cache when scheduling so when the processes bounce from
>> processor to processor, it is because the process' data is already 
>> out of the
>> cache (and there is really no gain in keeping the process in the same
>> processor, esp. when that processor is busy with another process).
>>
>> Thanks in advance,
>>  -- Diego.
>>
>> El Jueves, 21 de Junio de 2007 12:27, Darius Buntinas escribió:
>>> In linux there's a command called numactl which can be used to 
>>> execute a
>>> process and bind it to a physical processor.  Unfortunately, it looks
>>> like pbind can only bind a process once it has already been 
>>> started.  If
>>> you can find a command on sun similar to numactl on linux you can do
>>> something like what I do with numactl.
>>>
>>> With numactl one can do something like this to bind each process to a
>>> different processor:
>>>
>>> mpiexec -n 1 numactl --physcpubind=0 -- myapp myapparg : -n 1 numactl
>>> --physcpubind=1 -- myapp myapparg : -n 1 numactl --physcpubind=2 --
>>> myapp myapparg
>>>
>>> etc.
>>>
>>> Of course that's messy, so a more general solution would be to write a
>>> script called, e.g. execbind, to do that:
>>>
>>> numactl --physcpubind=`expr $PMI_RANK % $PROCS_PER_NODE` -- $@
>>>
>>> Where $PROCS_PER_NODE is the number of processors on each node of your
>>> cluster, and $PMI_RANK is set by mpiexec.
>>>
>>> Then, if you wanted to start 16 processes on a cluster of machines with
>>> 4 cores each, you could simply do:
>>>
>>> mpiexec -n 16 -env PROCS_PER_NODE 4 execbind myapp myapparg
>>>
>>> Darius
>>>
>>> Christina Patrick wrote:
>>>> Is it possible for me to modify the Python script (mpiexec) in such a
>>>> way that I use the pbind command to bind each instance of the 
>>>> executing
>>>> program to a different processor? I would like to give that a shot.
>>>>
>>>> Warm Regards,
>>>> Christina.
>>>>
>>>>
>>>> On 6/20/07, *Rajeev Thakur* <thakur at mcs.anl.gov
>>>> <mailto:thakur at mcs.anl.gov>> wrote:
>>>>
>>>>     MPICH2 leaves the scheduling of processes to the OS. If the OS has
>>>>     some way
>>>>     to bind processes to processors, you could try using it.
>>>>
>>>>     Rajeev
>>>>
>>>>> -----Original Message-----
>>>>> From: owner-mpich-discuss at mcs.anl.gov
>>>>
>>>>     <mailto:owner-mpich-discuss at mcs.anl.gov>
>>>>
>>>>> [mailto:owner-mpich-discuss at mcs.anl.gov
>>>>
>>>>     <mailto:owner-mpich-discuss at mcs.anl.gov>] On Behalf Of
>>>>
>>>>> Christina Patrick
>>>>> Sent: Wednesday, June 20, 2007 4:12 PM
>>>>> To: mpich-discuss-digest at mcs.anl.gov
>>>>
>>>>     <mailto:mpich-discuss-digest at mcs.anl.gov>
>>>>
>>>>> Subject: [MPICH] Binding and instance of the MPI program to a
>>>>> particular processor
>>>>>
>>>>> Hi everybody,
>>>>>
>>>>> I am having a 8 processor Solaris 9 machine and I want to
>>>>> execute an MPI program on it. The problem is that the tasks
>>>>> created by mpiexec keep migrating on the different
>>>>> processors. Since it is only one machine, there is only one
>>>>> instance of the mpdboot daemon running on the machine. Hence
>>>>> when I execute the below command on the machine with 8
>>>>> processors, I get an output that says:
>>>>>
>>>>> (For example, if the MPI program name is "finalized")
>>>>> # mpiexec -n 8 ./finalized
>>>>> 0:  No Errors
>>>>>
>>>>> When I examined the system using the "prstat" command, I
>>>>> observed that the tasks are migrating between the different
>>>>> processors.
>>>>>
>>>>> Is there any why in which I could bind each instance of the
>>>>> MPI program to a different processor.
>>>>>
>>>>> Your suggesstions and help is appreciated,
>>>>>
>>>>> Thanks,
>>>>> Christina.
>>
>
>