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Subject: Re: [OMPI users] (no subject)
From: San B (forum.san_at_[hidden])
Date: 2013-11-02 03:40:52


Yes MM... But here a single node has 16cores not 64 cores.
The 1st two jobs were with OMPI-1.4.5.
      16 cores of single node - 3692.403
      16 cores on two nodes (8 cores per node) - 12338.809

The 1st two jobs were with OMPI-1.6.5.
      16 cores of single node - 3547.879
      16 cores on two nodes (8 cores per node) - 5527.320

      As others said, due to shared memory communication the single node
job is running faster, but I was expecting a slight difference between 1 &
2 nodes - which is taking 60% more time here.

On Thu, Oct 31, 2013 at 8:19 PM, Ralph Castain <rhc_at_[hidden]> wrote:

> Yes, though the degree of impact obviously depends on the messaging
> pattern of the app.
>
> On Oct 31, 2013, at 2:50 AM, MM <finjulhich_at_[hidden]> wrote:
>
> Of course, by this you mean, with the same total number of nodes, for e.g.
> 64 process on 1 node using shared mem, vs 64 processes spread over 2 nodes
> (32 each for e.g.)?
>
>
> On 29 October 2013 14:37, Ralph Castain <rhc_at_[hidden]> wrote:
>
>> As someone previously noted, apps will always run slower on multiple
>> nodes vs everything on a single node due to the shared memory vs IB
>> differences. Nothing you can do about that one.
>>
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