[Mpi3-rma] MPI RMW operations

[Howard Pritchard]

Hello Brian,

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.
>  
>
This is a good point.  Given the way it is illegal to have an 'epoch within
an epoch' currently, I think this should continue to be enforced.  So
I would prefer the "it wouldn't", otherwise we risk making rma epoch
semantics more complicated.

>Also, is there any reason we're not using the standard OP defines?
>  
>
We could use the standard ones for the non-fetching operations.  For
fetching operations we could re-use them as long as it was clearly defined
what was returned to the initiator in 'result_addr'.  Some new operations
would have to be added for compare and swap  and masked compare
and swap though.

Howard

>Brian
>
>On Mar 25, 2008, at 9:14 AM, Howard Pritchard wrote:
>
>  
>
>>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:
>>
>>    
>>
>>>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:
>>>
>>>
>>>
>>>      
>>>
>>>>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.
>>>>
>>>>
>>>>
>>>>
>>>>_______________________________________________
>>>>mpi3-rma mailing list
>>>>mpi3-rma at lists.mpi-forum.org
>>>>http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
>>>>
>>>>
>>>>
>>>>        
>>>>
>>>
>>>      
>>>
>>--
>>
>>Howard Pritchard
>>Cray Inc.
>>
>>
>>_______________________________________________
>>mpi3-rma mailing list
>>mpi3-rma at lists.mpi-forum.org
>>http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi3-rma
>>
>>    
>>
>
>  
>


-- 

Howard Pritchard 
Cray Inc.