[Mpi3-rma] [EXTERNAL] Re: Memory barriers in MPI_WIN_LOCK_ALL mode

Pavan Balaji balaji at mcs.anl.gov
Tue Oct 30 11:06:29 CDT 2012

On 10/30/2012 10:50 AM, Underwood, Keith D wrote:
>> for shared memory, we do agree that you need some sort of memory
>> barrier within the GET operation for all local GETs.  I agree that
>> on x86-like architectures, this might not be needed.
> Why is it in the GET instead of the sync that precedes it?  Without
> the sync, the memory barrier in the GET does not have value, does
> it?

My point with the example I gave is that the synchronization might not 
be an RMA Win_sync.  In my example, it was the hand waving.

If we require the user to do MPI_WIN_SYNC before doing an MPI_GET from 
local windows, the shared memory problem will be resolved.  However, as 
you pointed out, this still doesn't resolve the network problem unless 
the FLUSH guarantees that the data is available in remote memory and not 
stuck in the PCIe complex somewhere.

  -- Pavan

Pavan Balaji

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