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Subject: Re: [OMPI users] MPI_Reduce performance
From: Eugene Loh (eugene.loh_at_[hidden])
Date: 2010-09-10 10:27:02


Richard Treumann wrote:

Hi Ashley

I understand the problem with descriptor flooding can be serious in an application with unidirectional data dependancy. Perhaps we have a different perception of how common that is.
Ashley speculated it was a "significant minority."  I don't know what that means, but it seems like it is a minority (most computations have causal relationships among the processes holding unbounded imbalances in check) and yet we end up seeing these exceptions.
I think that adding some flow control to the application is a better solution than semantically redundant barrier.
It seems to me there is no difference.  Flow control, at this level, is just semantically redundant synchronization.  A barrier is just a special case of that.