[mpich-discuss] Question about mpich bandwidth vs message-size plot

Jeff Hammond jeff.science at gmail.com
Tue Nov 26 21:45:17 CST 2019

There is no way for internode latency to be less than ~1 us. Thus, I
conclude you measure intranode results with MPICH and internode with
everything else.

Check your mpirun commands and try again.


On Tue, Nov 26, 2019 at 10:57 AM Sajid Ali via discuss <discuss at mpich.org>

> Hi MPICH-developers,
> I’ve been trying to benchmark mpi software currently available on my univ.
> cluster with OSU micro benchmarks. I used this script to build and run the
> benchmark :
> https://github.com/s-sajid-ali/nu-quest-mpi/blob/master/curr_mpi_bench/submit.sh
> And here is a plot of the results I obtained :
> [image: curr_mpi.png]
> Could someone give me a clue as to why the behaviour of mpich bandwidth vs
> latency is so odd ? Why does the bandwidth increase first and then fall off
> at high message sizes?
> I’m also attaching the config.log for this particular mpich build which
> seems to indicate that MPICH was built with ch3 and nemesis:tcp. Does this
> mean that it didn’t pick up the infiniband libraries or that it is somehow
> using IPoIB? Is there a way to get this information ?
> Thanks in advance for the help!
> --
> Sajid Ali | PhD Candidate
> Applied Physics
> Northwestern University
> s-sajid-ali.github.io
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Jeff Hammond
jeff.science at gmail.com
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