[mpiwg-rma] Problems with RMA synchronization in combination with load/store shared memory accesses

Rolf Rabenseifner rabenseifner at hlrs.de
Fri Feb 21 05:07:37 CST 2014

Dear member of the RMA group and especially the mpich developers,

I have real problems with the new shared memory in MPI-3.0,
i.e., the load/stores together with the RMA synchronization
causes wrong execution results.

The attached 
    1sided_halo_C_mpich_problems_rabenseifner.tar.gz or .zip

- 1sided/halo_1sided_put_win_alloc.c

  The basis that works. It uses MPI_Put and MPI_Win_fence for 
  duplex left/right halo communication.

- 1sided/halo_1sided_store_win_alloc_shared.c

   This is the same, but a shared memory window is used and
   the MPU_Put is substituted by storing the data in the 
   neighbors window. Same MPI_Win_fence with same assertions.

   This does not work, although I'm sure that my assertions are correct.

   Known possibilities:
   - I'm wrong and was not able to understand the assertions 
     on MPI-3.0 p452:8-19.
   - I'm wrong because it is invalid to use the MPI_Win_fence
     together with the shared memory windows. 
   - mpich has a bug.
   (The first two possibilities are the reason, why I use this 
    Forum email list)

- 1sided/halo_1sided_store_win_alloc_shared_w-a-cray.c

   This is a work-around-for Cray that works on our Cray 
   It also runs on another mpich installation.

- 1sided/halo_1sided_store_win_alloc_shared_pscw.c

   Here, MPI_Win_fence is substituted by Post-Start-Complete-Wait
   and it does not work for any assertions.

   Same possibilities as above.

- 1sided/halo_1sided_store_win_alloc_shared_query.c
- 1sided/halo_1sided_store_win_alloc_shared_query_w-a-cray.c

   Same as halo_1sided_store_win_alloc_shared.c
   but non-contigues windows are used.
   Same problems as above.
- 1sided/halo_1sided_store_win_alloc_shared_othersync.c

   This version uses the synchronization according to
   #413 and it is tested and works on two platforms.

Best regards

Dr. Rolf Rabenseifner . . . . . . . . . .. email rabenseifner at hlrs.de
High Performance Computing Center (HLRS) . phone ++49(0)711/685-65530
University of Stuttgart . . . . . . . . .. fax ++49(0)711 / 685-65832
Head of Dpmt Parallel Computing . . . www.hlrs.de/people/rabenseifner
Nobelstr. 19, D-70550 Stuttgart, Germany . . . . (Office: Room 1.307)
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