[mpich-discuss] mpi query

[SHEETAL MALU]

Respected Sir,

When I am trying to create 8 no. of process on 2
servers having 8 processor each, like process(0,2,4,6)  on server1 and
remaining process(1,3,5,7) on server2 then the results for
MPI_Allgather are faster upto 16Kb of data and for data size greater
than 16Kb MPI_Gather+MPI_Bcast performs faster.

If I try to
create process(0,1,2,3) on server1 and process(4,5,6,7) on server2 then
MPI_Gather+MPI_Bcast is faster than MPI_Allgather.Sir, I am unable to
get reason for this because MPI_Allgather should perform faster than
MPI_Gather+MPI_Bcast but I am getting the contradictory results when
creating process(0,1,2,3) on server1 and process(4,5,6,7) on server2.

Does protocol switch from eager to rendezvous also affects the collective operations like in point to point
 communication.

Please Sir, let me know the solution.

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