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

[Jim Dinan]

Rolf,

This line is incorrect: MPI_Win_fence(MPI_MODE_NOSTORE +
MPI_MODE_NOPRECEDE, win_rcv_buf_left );

You need to do a bitwise OR of the assertions (MPI_MODE_NOSTORE |
MPI_MODE_NOPRECEDE).

In halo_1sided_store_win_alloc_shared.c, you are doing stores within the
epoch, so MPI_MODE_NOSTORE looks like an incorrect assertion on the closing
fence.

Following the Fence epoch, you are reading from the left/right recv
buffers.  That also needs to be done within an RMA epoch, if you are
reading non-local data.

 ~Jim.


On Fri, Feb 21, 2014 at 6:07 AM, Rolf Rabenseifner <rabenseifner at hlrs.de>wrote:

> 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
> contains
>
> - 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
>    and does not use MPI_MODE_NOPRECEDE and MPI_MODE_NOSUCCEED.
>    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
> Rolf
>
> --
> 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)
>
> _______________________________________________
> mpiwg-rma mailing list
> mpiwg-rma at lists.mpi-forum.org
> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpiwg-rma
>
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