[mpich-discuss] allgatherv

[Halim Amer]

Looking at the code, for long messages the same ring algorithm is used 
for long/medium messages regardless of whether the number of processes 
is a power of two or not. The comment is wrong. We will fix it, but in 
general one shouldn't rely solely on code comments and should look at 
the code itself.

--Halim
www.mcs.anl.gov/~aamer

On 5/9/16 12:21 PM, Jen B wrote:
> Hello,
>
> I am looking at allgatherv.c from:
>
> git.mpich.org/mpich.git/tree/HEAD:/src/mpi/coll
> <http://git.mpich.org/mpich.git/tree/HEAD:/src/mpi/coll>
>
> It says the following:
>
> "For short or medium-size messages and power-of-two no. of processes,
> we use the recursive doubling algorithm.
> ...
> For long messages or medium-size messages and non-power-of-two
> no. of processes, we use a ring algorithm.
> ..."
>
> Could someone please tell me what algorithm is used when we have "long
> messages and power-of-two no. of processes"? Thanks a lot!
>
> Best,
> Jen
>
>
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