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Subject: Re: [OMPI users] How to force eager behavior during Isend?
From: Barry Rountree (rountree_at_[hidden])
Date: 2008-12-08 12:50:05


---- Original message ----
>Date: Mon, 8 Dec 2008 11:47:19 -0500
>From: George Bosilca <bosilca_at_[hidden]>
>Subject: Re: [OMPI users] How to force eager behavior during Isend?
>To: Open MPI Users <users_at_[hidden]>
>
>Barry,
>
>These values are used deep inside the Open MPI library, in order to
>define how we handle the messages internally. From a user perspective
>you will not see much difference.

Well, this user does.... ;-) I'm working on how to slow the processor when the library is blocked, and it's my understanding from the state-of-the-openmpi-union talk at SC that blocking progress functionality wouldn't be implemented for a while yet. So I'm making do with home-rolled solutions, one of which is figuring out the expected time needed to transfer a certain amount of data, then assuming any time spent in the library in excess of that is blocking time.

The fact that the behavior of Isend and Irecv is determined by message size makes this a little more difficult, so I wanted to be able to either force eager sending in nearly all cases or turn off eager sending entirely. Once the algorithm is working in these simpler cases I can go back and make it work for the optimized case.

> Moreover, checking the number of
>completed requests returned by MPI_Wait* if definitively not the most
>accurate way to test this.

I'm not sure what you mean here. My PMPI library uses timestamps to determine how long was spent inside and outside the library. If the Isends are eager, very little time should be spent in the corresponding Wait, correct?

> If you really want to see that these
>parameters are taken in account you will need to a lower level
>interface, such as PERUSE.
>

Ok, that looks like it could be useful. Google has your "Implementation and Usage" paper as the first hit; I'll read p on that.

Barry

> george.