[mvapich-discuss] collectives fail under mvapich2-1.0 (fwd)

[Edmund Sumbar]

wei huang wrote:
> Hi Ed,
> 
> We look into the problem more wrt one sided issues. However, we don't see
> the program hang in the MPI library. Actually the program is not hanging.
> But somehow for MPI_Win_test, we find the following code:
> 
>   if (get_measurement_rank() == 0) {
>     reduced_group = exclude_rank_from_group(0, onesided_group);
>     mpiassert = extract_onesided_assertions(assertion, "MPI_Win_post");
>     MPI_Win_post(reduced_group, mpiassert, onesided_win);
> 
>     start_time = start_synchronization();
>     MPI_Win_test(onesided_win, &flag);
>     end_time = stop_synchronization();
>     if (flag == 0)
>       MPI_Win_wait(onesided_win);
>   }
>   else {
>     reduced_group = exclude_all_ranks_except_from_group(0, onesided_group);
>     mpiassert = extract_onesided_assertions(assertion, "MPI_Win_start");
>     MPI_Win_start(reduced_group, mpiassert, onesided_win);
>     if (do_a_put)
>       MPI_Put(get_send_buffer(), count, datatype, 0, get_measurement_rank(),
>               count, datatype, onesided_win);
>     MPI_Win_complete(onesided_win);
>     start_synchronization();
>     stop_synchronization();
>   }
> 
> And the test is spending more and more in in start_synchronization(),
> which seems to calculate a certain timestamp, and busily reads wtime()
> until we reach that timestamp. We find that start_synchronization() is
> taking longer and longer time, and finally will spend tens of seconds
> before it returns. We are not sure how the timestamp is calculated, so we
> cc this email to SkaMPI team and hope they can give some insights here.

Hi Wei,

Thank you for looking into this issue.

This may or may not be related, but the SKaMPI document
describing their new timing approach for collectives can
be found at

   http://www.springerlink.com/content/7ygll9u0h02t8mth/fulltext.pdf


-- 
Ed[mund [Sumbar]]
AICT Research Support, Univ of Alberta