[mpich-devel] Suboptimal MPI_Allreduce() for intercommunicators

[Lisandro Dalcin]

On 30 April 2014 18:56, Rajeev Thakur <thakur at mcs.anl.gov> wrote:
> It was probably done that way to avoid the need for memory allocation, but can you add a ticket in Trac and we will look at it.
>

https://trac.mpich.org/projects/mpich/ticket/2074

>
> (For example, on one side of the intercommunicator sendbuf=1 byte, recvbuf=1 gigabyte; on the other side, sendbuf=1 gigabyte, recvbuf=1 byte)
>

For Allreduce, you cannot have 1 byte/  1gigabyte at each side.


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Lisandro Dalcin
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