HI Brian, On Mar 25, 2008, at 11:22 AM, Brian W. Barrett wrote:

That makes sense. How would an MPI_Rmw() call with the IMPLICIT epoch interact with explicit epochs? If the answer is "it wouldn't", I think that's valid. We just need to state it.

I would think the behavior would be undefined or "it wouldn't".

Also, is there any reason we're not using the standard OP defines?

We would need additional operations for RMW/2 (as shown) and restrict other operations that don't apply within the standard. I would also want to carefully look at the implementation costs for using the standard OP defines. - Galen

Brian

On Mar 25, 2008, at 9:14 AM, Howard Pritchard wrote:

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Hello Brian,

That was the idea.

The problem as we saw it is that in non-mpi shared memory applications, atomic memory operations are typically used for lightweight synchronization. Having to always use potentially heavyweight lock/ unlock sequences seems to defeat the purpose of adding rmw operations to the mpi specification.

This is a special case of the more general discussion that we should have about global visibility of rma operations, etc.

Howard

Brian W. Barrett wrote:

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If MPI_MODE_PASSIVE_EPOCH_IMPLICIT is not given, is synchronization explicit using the standard epoch functions?

Brian

On Mar 24, 2008, at 9:09 PM, Shipman, Galen M. wrote:

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Howard and I have been working on the RMW operations listed below for consideration.

- Galen Shipman - ORNL

Single operand RMW operations

MPI_Rmw(void *operand_addr, int count, MPI_Datatype datatype, void *result_addr, int target_rank, MPI_Aint target_disp, int assert, MPI_RMW_Op op, MPI_Win win)

Two operand RMW operations

MPI_Rmw2(void *operand_addr, int count, MPI_Datatype datatype, void *operand2_addr, void *result_addr, int target_rank, MPI_Aint target_disp, int assert, MPI_RMW_2_Op op, MPI_Win win)

MPI_RMW_Op Predefined RMW single operand operations The following predefined operations are supplied for MPI_RMW and related functions. These operations are invoked by placing the following in op.

Name Meaning

MPI_RMW_INC increment MPI_RMW_PROD product MPI_RMW_SUM sum MPI_RMW_LAND logical and MPI_RMW_LOR logical or MPI_RMW_LXOR logical xor MPI_RMW_BAND binary and MPI_RMW_BOR binary or MPI_RMW_BXOR binary xor MPI_RMW_SWAP swap value

MPI_RMW_2_Op Predefined RMW two operand operations

Name Meaning

MPI_RMW2_MASK_SWAP swap masked bits MPI_RMW2_COMP_SWAP compare and swap

Note: MPI_RMW2_COMP_SWAP is an equality comparison, we may wish to consider multiple comparison operations such as >, >=, <, <=, ==, <>.

Both MPI_Rmw and MPI_Rmw2 take an assert argument. When assert == MPI_MODE_PASSIVE_EPOCH_IMPLICIT MPI_Rmw/2 is equivalent to:

MPI_Win_lock(target_rank,0,win); MPI_Rmw(.....); MPI_Win_unlock(target_rank,0,win);

When assert == MPI_MODE_PASSIVE_EPOCH_IMPLICIT | MPI_MODE_NOCHECK the MPI library knows that the window lock at the target need not be acquired.

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--

Howard Pritchard Cray Inc.

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-- Brian W. Barrett Dept. 1422: Scalable Computer Architectures Sandia National Laboratories

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