[mpich-discuss] mpi_scatter

[Jen B]

Here is the sample of information that I need. For example, in that paper
for long messages (>=512KB) and any number of processes "allgather" uses
the ring algorithm. Can anyone give me similar answer (algorithm used in
MPICH2) for mpi_scatter (when we have long messages, and for both power of
two and non power of two number of processes)? Thanks.

Best,
Jen

On Thu, Dec 3, 2015 at 2:25 PM, Jeff Hammond <jeff.science at gmail.com> wrote:

> I don't know exactly what information you want, but you will find a lot of
> useful comments in the source files here:
> http://git.mpich.org/mpich.git/tree/HEAD:/src/mpi/coll.  In particular,
> if you run 'grep -i "we use" *.c', you will see statements about
> Rabenseifer's algorithm, Bruck's algorithm, recursive doubling, pairwise
> exchange, etc.
>
> Best,
>
> Jeff
>
> On Thu, Dec 3, 2015 at 8:24 AM, Jen B <jenbna at gmail.com> wrote:
>
>> Hello,
>>
>> I am trying to understand how the mpi_scatter is implemented according to
>> MPICH2 for long messages. I went through the paper of R. Thakur, et al.,
>> titled "Optimization of Collective Communication Operations in MPICH." It
>> is stated there that for long messages mpi_bcast is composed of scatter and
>> allgather (where latter two are based on the Van de Geijn's algorithm).
>> However I wasn't able to find the mpi_scatter details. Could you please
>> explain this? Also, the another thing is that I think for long messages
>> (that are not divisible exactly by the number of processes) this part would
>> use a scatterv + allgatherv. Am I right? Thank you!
>>
>> Best,
>> Jen
>>
>>
>>
>>
>>
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>
>
>
> --
> Jeff Hammond
> jeff.science at gmail.com
> http://jeffhammond.github.io/
>
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