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Subject: Re: [OMPI users] difference between single and double precision
From: Mathieu Gontier (mathieu.gontier_at_[hidden])
Date: 2010-12-16 05:17:27


Does the env. var. works to overload it:
export OMPI_MCA_btl_sm_eager_limit=40960

In that case, I can deal with it.

On 12/16/2010 11:14 AM, Mathieu Gontier wrote:
> Hi all,
>
> We have lead some tests and the option btl_sm_eager_limit has a
> positive consequence on the performance. Eugene, thank you for your
> links.
>
> Now, to offer a good support to our users, we would like to get the
> value of this parameters at the runtime. I am aware I can have the
> value running ompi_info like following:
> ompi_info --param btl all | grep btl_sm_eager_limit
>
> but can I get the value during the computation when I run mpirun -np
> 12 --mca btl_sm_eager_limit 8192 my_binary? This value could be
> compared with the buffer size into my code and some warning put into
> the output.
>
> Any idea?
>
> On 12/06/2010 04:31 PM, Eugene Loh wrote:
>> Mathieu Gontier wrote:
>>
>>> Nevertheless, one can observed some differences between MPICH and
>>> OpenMPI from 25% to 100% depending on the options we are using into
>>> our software. Tests are lead on a single SGI node on 6 or 12
>>> processes, and thus, I am focused on the sm option.
>>
>> Is it possible to narrow our focus here a little? E.g., are there
>> particular MPI calls that are much more expensive with OMPI than
>> MPICH? Is the performance difference observable with simple
>> ping-pong tests?
>>
>>> So, I have two questions:
>>> 1/ does the option--mca mpool_sm_max_size=XXXX can change something
>>> (I am wondering if the value is not too small and, as consequence, a
>>> set of small messages is sent instead of a big one)
>>
>> There was recent related discussion on this mail list.
>> http://www.open-mpi.org/community/lists/users/2010/11/14910.php
>>
>> Check the OMPI FAQ for more info. E.g.,
>> http://www.open-mpi.org/faq/?category=sm
>>
>> This particular parameter disappeared with OMPI 1.3.2.
>> http://www.open-mpi.org/faq/?category=sm#how-much-use
>>
>> To move messages as bigger chunks, try btl_sm_eager_limit and
>> btl_sm_max_send_size:
>> http://www.open-mpi.org/faq/?category=sm#more-sm
>>
>>> 2/ is there a difference between --mca btl tcp,sm,self and --mca btl
>>> self,sm,tcp (or not put any explicit mca option)?
>>
>> I think tcp,sm,self and self,sm,tcp will be the same. Without an
>> explicit MCA btl choice, it depends on what BTL choices are available.
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