[gmx-users] Parallel Gromacs Benchmarking with Opteron Dual-Core & Gigabit Ethernet

[Erik Lindahl]

Hi,

> I agree with you about the GbE sharing between 4 cores degardes the
> performance. Fortunately, every Cluster node has two GbE ports. I
> want to know, can I configure lamd in such a manner that every  
> processor
> on every node (with two cores) uses one of these ports for its
> communication purposes? And if this is possible, could you please  
> give me
> some hints or guidance to start this configuration on the cluster?
> And finally, can you expect any scalability improvements by taking  
> this
> approach?


Built-in network cards are usually of lower quality, so there's  
probably only a single processor controlling both ports, and since  
the card probably only has a single driver requests might even be  
serialized.

If you have lots of available ports on your gigabit switches and both  
switches+cards support "port trunking" you could try to connect two  
cables to each node and get a virtual 2Gb bandwidth connection. For  
more advanced stuff you'll have to consult the lam-mpi mailing list,  
although I'd be (quite pleasantly) surprised if it's possible to  
tweak gigabit performance a lot!

Cheers,

Erik