[mpich-discuss] allgatherv

Thakur, Rajeev thakur at mcs.anl.gov
Mon May 9 12:27:35 CDT 2016


Read it this way with the parenthesis:

For long messages or (medium-size messages and non-power-of-two no. of processes)


> On May 9, 2016, at 12:21 PM, Jen B <jenbna at gmail.com> wrote:
> 
> Hello,
> 
> I am looking at allgatherv.c from:
> 
> 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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