[mpich-discuss] thread MPI calls

[chong tan]

we just completed 1 partiticular tests using SERIALIZED, and that make no difference (compared to
MULTIPLE).  

I also check ANY_TAG, we are not using that anymore.  SO, we use both source and tag.  Given
that there are only 3 producers , N^2 algorithm does not worry me.

tan

 

________________________________
From: Pavan Balaji <balaji at mcs.anl.gov>
To: mpich-discuss at mcs.anl.gov
Sent: Tuesday, July 28, 2009 3:09:18 PM
Subject: Re: [mpich-discuss] thread MPI calls


> yes, we are using source, but we are using ANY_TAG.  We can't try ANY_SOURCE as
> source is significant, unless I make chanages to the data package.

I'd suggest that you either use both ANY_SOURCE and ANY_TAG, or neither. From an MPI implementation's perspective, always using ANY_SOURCE + ANY_TAG is best for performance, since all incoming messages will have a constant queue search time. On the other hand, if you don't use either of them, then it'll allow the MPI implementation to use multiple queues instead of a single queue, which reduces the search time quite a bit as well (constant time in most cases as well). Using one of them as a wild-card and the other as a non-wild-card is the worst-case scenario.

> We can try SERIALIZED, but that will block our next strategy which requires MULTIPLE.

For now, this will at least tell us whether MPI's locks are the bottleneck or if there's some other bottleneck.

If this does show up as a problem, we can try to profile your application with MPE and/or rlog (MPICH2's internal profiling tool). It'll give you a nice graphical output on the amount of time spent in each routine. Very useful for performance debugging.

-- Pavan

-- Pavan Balaji
http://www.mcs.anl.gov/~balaji



      
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