If a hardware can implement MPI_SUM, it should be able to implement MPI_SUM with 0 as well. But that’s not a generic solution. Jeff: at some point you were planning to bring in a ticket which does more combinations of operations than just same_op and no_op. Maybe it’s worthwhile bringing that up again? — Pavan On Mar 10, 2014, at 9:26 PM, Jim Dinan <[email protected]> wrote:

Maybe there's a loophole that I'm forgetting?

On Mon, Mar 10, 2014 at 9:43 PM, Jeff Hammond <[email protected]> wrote: How the hell can I do GA or SHMEM then? Roll my own mutexes and commit perf-suicide?

Jeff

Sent from my iPhone

On Mar 10, 2014, at 8:32 PM, Jim Dinan <[email protected]> wrote:

...

You can't use replace and sum concurrently at a given target address.

~Jim.

On Mon, Mar 10, 2014 at 4:30 PM, Jeff Hammond <[email protected]> wrote: Given the following, how do I use MPI_NO_OP, MPI_REPLACE and MPI_SUM in accumulate/atomic operations in a standard-compliant way?

accumulate_ops — if set to same_op, the implementation will assume that all concurrent accumulate calls to the same target address will use the same operation. If set to same_op_no_op, then the implementation will assume that all concurrent accumulate calls to the same target address will use the same operation or MPI_NO_OP. This can eliminate the need to protect access for certain operation types where the hardware can guarantee atomicity. The default is same_op_no_op.

We discuss this before and the resolution was not satisfying to me.

Thanks,

Jeff

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