On 3/2/11 1:50 PM, "James Dinan" <[email protected]> wrote:

On 03/02/2011 01:48 PM, Barrett, Brian W wrote:

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On 3/2/11 9:47 AM, "James Dinan"<[email protected]> wrote:

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When we state that accumulates with the same operation are non-conflicting, should I be interpreting this as CAS is only non-conflicting with other CAS operations? This is a bit of a stretch since CAS doesn't take an op argument, but I suppose it's doable. Some text to help the reader make this connection for CAS would definitely help.

CAS is defined as an accumulate operation (pg 1, ln 38--41), so yes, CAS should be interpreted as a different operation than MPI_REPLACE or MPI_SUM or... I personally think this is obvious, but have no objection to an additional sentence in the accumulate_ops info key specifying this. I believe that's the only place in the current text where operation conflicts are discussed, but I could be wrong.

I think there are two ways to interpret the current text:

1. CAS defines a new accumulate op that can only be performed by MPI_Compare_and_swap, thus it is only non-conflicting with itself.

2. MPI_Compare_and_swap has a fixed op=MPI_REPLACE and it is non-conflicting with all other accumulate calls if op=MPI_REPLACE is given.

Number 1 seems tricky to me because Get_accumulate with op=MPI_REPLACE does an unconditional SWAP. Number 2 seems to mesh better with existing accumulate operations, but do concurrent CAS, SWAP, and REPLACE operations play nice?

That's true, I guess I'm ok defining CAS as on MPI_REPLACE operation. That would mean that you could use CAS, Accumulate(REPLACE), Get_Accumulate(REPLACE), and Get_Accumulate(NO_OP) to the same address, with no other operations legal. That doesn't bother me too much, and probably makes sense. As an aside, it's not clear in the current text which is the default for accumulate_ops: same_op or same_op_no_op. The semantics section still defines same_op, but that seems to go agains the use of info keys to relax requirements on the implementation. Brian -- Brian W. Barrett Dept. 1423: Scalable System Software Sandia National Laboratories