Hi,

Note that it matters a lot how far you want to parallelize and what
kind of runs would you do? 10 GbE with RoCE may well be enough to
scale across a couple of such nodes, especially if you can squeeze PME
into a single node and avoid the MPI collectives across the network.
You may not even see much difference between, say 10 GbE + RoCE and
some older IB like CX-3 FDR. However, if you want to run at larger
strong scale with short time/step, even the P-to-P communication of
halo-exchange will become a bottleneck on slower networks as
communications gets purely latency-bound.

I have no data myself nor first-hand experience, but there are some
results out there, e.g.
http://www.hpcadvisorycouncil.com/pdf/GROMACS_Analysis_Intel_E5_2697v3_K40_K80_GPUs.pdf
http://www.hpcadvisorycouncil.com/pdf/GROMACS_Analysis_Intel_E5_2697v3.pdf

Take these with a grain of salt, however, as they seem to show
different data in places, e.g. slide 10 of the former suggests that
EDR IB is >3x faster already from 2 nodes with RF, but the latter
suggests that on 2-4 nodes 10 GbE / 40 GbE is not too awful (though
compared to EDR IB).

Cheers,
--
Szilárd


On Mon, Mar 12, 2018 at 9:38 AM, Mark Abraham <mark.j.abra...@gmail.com> wrote:
> Hi,
>
> GROMACS doesn't much care about bandwidth, but rather message latency and
> message injection rate (which in some cases depends on what else is sharing
> the network). For those, even high quality gigabit ethernet *can* be good
> enough, so likely any Infiniband product will be just fine. Unfortunately
> we don't have access to any resource that would permit us to gather
> comparative data.
>
> Mark
>
> On Mon, Mar 12, 2018 at 9:09 AM Simon Kit Sang Chu <simoncks1...@gmail.com>
> wrote:
>
>> Hi everyone,
>>
>> Our group is also interested in purchasing cloud GPU cluster. Amazon only
>> supplies GPU cluster connected by 10Gb/s bandwidth. I notice this post but
>> there is no reply by far. It would be nice if someone give any clue.
>>
>> Regards,
>> Simon
>>
>> 2018-03-06 1:31 GMT+08:00 Daniel Bauer <ba...@cbs.tu-darmstadt.de>:
>>
>> > Hello,
>> >
>> > In our group, we have multiple identical Ryzen 1700x / Nvidia GeForce
>> > 1080 GTX computing nodes and think about interconnecting them via
>> > InfiniBands.
>> >
>> > Does anyone have Information on what Bandwidth is required by GROMACS
>> > for communication via InfiniBand (MPI + trajectory writing) and how it
>> > scales with the number of nodes?
>> >
>> > The mainboards we are currently using can only run one PCIe slot with 16
>> > lanes. When using both PICe slots (GPU+InfiniBand), they will run in
>> > dual x8 mode (thus bandwidth for both GPU and InfiniBand will be reduced
>> > to 8 GB/s instead of 16 GB/s). Now we wonder if the reduced bandwidth
>> > will hurt GROMACS performance due to bottlenecks in GPU/CPU
>> > communication and/or communication via InfiniBand. If this is the case,
>> > we might have to upgrade to new mainboards with dual x16 support.
>> >
>> >
>> > Best regards,
>> >
>> > Daniel
>> >
>> > --
>> > Daniel Bauer, M.Sc.
>> >
>> > TU Darmstadt
>> > Computational Biology & Simulation
>> > Schnittspahnstr. 2
>> > 64287 Darmstadt
>> > ba...@cbs.tu-darmstadt.de
>> >
>> > Don't trust atoms, they make up everything.
>> >
>> >
>> > --
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