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Date: Mon, 04 Aug 2014 11:50:54 +0200
From: magnum <>
Subject: Re: Splitting workload on multiple hosts

On 2014-08-04 05:59, Rich Rumble wrote:
> On Wed, Dec 11, 2013 at 6:59 PM, magnum <> wrote:
>>  From version 1.8 you can say "I'm node 427 out of 10000" using the option
>> "--node=427/10000". If some of your nodes are much stronger than others you
>> can tell them to do more work, eg. "--node=1-20/10000" will make this node
>> do the first 20 splices.
> So for an MPI host, would you also use "--node=1-8/16" on one host, and
> "--node=9-16/16" on the other? Assuming they are nearly identical and have
> 8 cores to use.

You would normally use MPI options and no --node option. Eg. "mpirun 
-host=alpha,bravo -np 16 ./john (...)" for splitting the job in 16 
processes over two hosts (so 8 on each).

However, if you want an MPI job to be part of a larger job (as in the 
original example) you'd do something like "mpirun -host=alpha,bravo -np 
16 ./john -node=1-16/10000 (...)".

Basically the syntax for MPI with --node is the same as for --fork with 
--node. So these two examples are equivalent in terms of work space:

./john -fork=16 -node=1-16/10000 (...)

mpirun -host=alpha,bravo -np 16 ./john -node=1-16/10000 (...)


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