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Subject: Re: [OMPI users] Binding to Core Warning
From: Saliya Ekanayake (esaliya_at_[hidden])
Date: 2014-02-26 19:29:54


I see, so if I understand correctly, the best scenario for threads would be
to bind 2 procs to sockets as --map-by socket:pe=4 and use 4 threads in
each proc.

Also, as you've mentioned binding threads to get memory locality, I guess
this has to be done at application level and not an option in OMPI

Thank you,
Saliya

On Wed, Feb 26, 2014 at 4:50 PM, Ralph Castain <rhc_at_[hidden]> wrote:

> Sorry, had to run some errands.
>
> On Feb 26, 2014, at 1:03 PM, Saliya Ekanayake <esaliya_at_[hidden]> wrote:
>
> Is it possible to bind to cores of multiple sockets? Say I have a machine
> with 2 sockets each with 4 cores and if I run 8 threads with 1 proc can I
> utilize all 8 cores for 8 threads?
>
>
> In that scenario, you won't get any benefit from binding as we only bind
> at the proc level (and binding to the entire node does nothing). You might
> want to bind your threads, however, as otherwise the threads will not
> necessarily execute local to any memory they malloc.
>
>
> Thank you for speedy replies
>
> Saliya
>
>
> On Wed, Feb 26, 2014 at 3:21 PM, Ralph Castain <rhc_at_[hidden]> wrote:
>
>>
>> On Feb 26, 2014, at 12:17 PM, Saliya Ekanayake <esaliya_at_[hidden]> wrote:
>>
>> I have a followup question on this. In our application we have parallel
>> for loops similar to OMP parallel for. I noticed that in order to gain
>> speedup with threads I've to set --bind-to none, otherwise multiple threads
>> will bind to same core giving no increase in performance. For example, I
>> get following (attached) performance for a simple 3point stencil
>> computation run with T threads on 1 MPI process on 1 node (Tx1x1).
>>
>> My understanding is even when there are multiple procs per node we should
>> use --bind-to none in order to get performance with threads. Is this
>> correct? Also, what's the disadvantage of not using --bind-to core?
>>
>>
>> Your best performance with threads comes when you bind each process to
>> multiple cores. Binding helps performance by ensuring your memory is always
>> local, and provides some optimized scheduling benefits. You can bind to
>> multiple cores by adding the qualifier "pe=N" to your mapping definition,
>> like this:
>>
>> mpirun --map-by socket:pe=4 ....
>>
>> The above example will map processes by socket, and bind each process to
>> 4 cores.
>>
>> HTH
>> Ralph
>>
>>
>> Thank you,
>> Saliya
>>
>>
>> On Wed, Feb 26, 2014 at 11:01 AM, Saliya Ekanayake <esaliya_at_[hidden]>wrote:
>>
>>> Thank you Ralph, I'll check this.
>>>
>>>
>>> On Wed, Feb 26, 2014 at 10:04 AM, Ralph Castain <rhc_at_[hidden]>wrote:
>>>
>>>> It means that OMPI didn't get built against libnuma, and so we can't
>>>> ensure that memory is being bound local to the proc binding. Check to see
>>>> if numactl and numactl-devel are installed, or you can turn off the warning
>>>> using "-mca hwloc_base_mem_bind_failure_action silent"
>>>>
>>>>
>>>> On Feb 25, 2014, at 10:32 PM, Saliya Ekanayake <esaliya_at_[hidden]>
>>>> wrote:
>>>>
>>>> Hi,
>>>>
>>>> I tried to run an MPI Java program with --bind-to core. I receive the
>>>> following warning and wonder how to fix this.
>>>>
>>>>
>>>> WARNING: a request was made to bind a process. While the system
>>>> supports binding the process itself, at least one node does NOT
>>>> support binding memory to the process location.
>>>>
>>>> Node: 192.168.0.19
>>>>
>>>> This is a warning only; your job will continue, though performance may
>>>> be degraded.
>>>>
>>>>
>>>> Thank you,
>>>> Saliya
>>>>
>>>> --
>>>> Saliya Ekanayake esaliya_at_[hidden]
>>>> Cell 812-391-4914 Home 812-961-6383
>>>> http://saliya.org
>>>> _______________________________________________
>>>> users mailing list
>>>> users_at_[hidden]
>>>> http://www.open-mpi.org/mailman/listinfo.cgi/users
>>>>
>>>>
>>>>
>>>> _______________________________________________
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>>>
>>>
>>>
>>> --
>>> Saliya Ekanayake esaliya_at_[hidden]
>>> Cell 812-391-4914 Home 812-961-6383
>>> http://saliya.org
>>>
>>
>>
>>
>> --
>> Saliya Ekanayake esaliya_at_[hidden]
>> Cell 812-391-4914 Home 812-961-6383
>> http://saliya.org
>> <3pointstencil.png>_______________________________________________
>>
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>>
>>
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>
>
>
> --
> Saliya Ekanayake esaliya_at_[hidden]
> Cell 812-391-4914 Home 812-961-6383
> http://saliya.org
> _______________________________________________
> users mailing list
> users_at_[hidden]
> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
>
> _______________________________________________
> users mailing list
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>

-- 
Saliya Ekanayake esaliya_at_[hidden]
Cell 812-391-4914 Home 812-961-6383
http://saliya.org