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Subject: Re: [OMPI devel] How to configure Open MPI on multi-port IB HCA cluster
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-03-03 13:46:39

On Mar 3, 2009, at 2:48 AM, Jie Cai wrote:

> We have installed a dual-port ConnectX HCA cluster with PIC-E 2.0
> slots,
> and each port represented as individual interface.
> How to configure the Open MPI and hardware system
> to correctly use the both ports for communication?

Open MPI should just see and use both ports automatically (assuming
that they are ACTIVE).

> Are we expecting to see wider bandwidth with Open MPI?

It depends on both your server and network setup.

The transfer rate across PCIe 2.0 cannot send enough data to keep 2
DDR HCA ports full. So it is unlikely that you will see much of a
bandwidth improvement.

Assuming that your 2 HCA ports are plugged into either 2 separate IB
subnets or different locations in the same subnet, you'll get a wider
dispersion of fragments across your network, potentially avoiding some
network congestion. But this behavior is very much dependent on what
else is occurring simultaneously elsewhere in your IB subnet, which is
likely to be application- / cluster-specific behavior.

> In order to see the improvement of bandwidth, do I need to specific
> configure Open MPI and the hardware?

To really get 2 x DDR performance, you likely need two separate busses
with two separate HCAs.

Jeff Squyres
Cisco Systems