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Subject: Re: [OMPI users] MPI_Bcast issue
From: Ashley Pittman (ashley_at_[hidden])
Date: 2010-08-11 10:22:12


On 11 Aug 2010, at 05:10, Randolph Pullen wrote:

> Sure, but broadcasts are faster - less reliable apparently, but much faster for large clusters.

Going off-topic here but I think it's worth saying:

If you have a dataset that requires collective communication then use the function call that best matches what you are trying to do, far to many people try and re-implement the collectives in their own code and it nearly always goes badly, as someone who's spent many years implementing collectives I've lost count of the number of times I've made someones code go faster by replacing 500+ lines of code with a single call to MPI_Gather().

In the rare case that you find that some collectives are slower than they should be for your specific network and message size then the best thing to do is to work with the Open-MPI developers to tweak the thresholds so a better algorithm gets picked by the library.

Ashley.

-- 
Ashley Pittman, Bath, UK.
Padb - A parallel job inspection tool for cluster computing
http://padb.pittman.org.uk