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From: Torsten Hoefler (htor_at_[hidden])
Date: 2007-10-12 07:00:10

> The code was pretty simple. I was trying to send 8MB data from one
> rank to other in a loop(say 1000 iterations). And then i was taking the
> average of time taken and was calculating the bandwidth.
> The above logic i tried with both mpirun-with-mca-parameters and without
> any parameters. And to my surprise, the performance was degrading when i
> was trying to manipulate.
That sounds strange. So did you re-use the communication buffers? Did
you try to run some existing benchmarks like Netpipe [1], IMB or
Netgauge [2]?

> Now I have another question in mind. Is it possible to have IB Hardware
> Multicast implementation in OpenMPI? I have gone through the
> issues/challenges for the same, but also read couple of people who have
> successfully done it for Ethernet/Giga-bit Ethernet and IPoIB ofcourse in
> experimental stage. Actually i want to contribute for it in OpenMPI and
> need the help for the same.
As far as I know, there are two groups/people working on this. Andy
Friedley implements a "traditional" ACK based approach (like the one
that the OSU folks published about some time ago) and I implemented a
new idea for extreme scale (see "A practically constant-time MPI
Broadcast Algorithm for large-scale InfiniBand Clusters with
Multicast" [3]). I know that my version is still unstable and has some
problems. But I'm working on this.



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