UCX is on the way into RH distro and will be available and ON by default 
(auto-detectable by OMPI build process) automatically in the near future.

Meanwhile, user can enable UCX by two methods:
1. Download & Install UCX from openucx.org and Build openmpi with it.
2. Download HPC-X from Mellanox site (openmpi pre-compiled and packaged with 
UCX) for distro of interest (User can re-compile the package with site default 
as well)

Also, for users using the latest MLNX_OFED, UCX is already part of it.


-----Original Message-----
From: devel <devel-boun...@lists.open-mpi.org> On Behalf Of Jeff Squyres 
(jsquyres) via devel
Sent: Tuesday, September 18, 2018 11:50 PM
To: Open MPI Developers List <devel@lists.open-mpi.org>
Cc: Jeff Squyres (jsquyres) <jsquy...@cisco.com>
Subject: Re: [OMPI devel] Announcing Open MPI v4.0.0rc1

On Sep 18, 2018, at 3:46 PM, Thananon Patinyasakdikul <tpati...@vols.utk.edu> 
> I tested on our cluster (UTK). I will give a thumb up but I have some 
> comments.
> What I understand with 4.0.
> - openib btl is disabled by default (can be turned on by mca)

It is disabled by default *for InfiniBand*.  It is still enabled by default for 
RoCE and iWARP.

> - pml ucx will be the default for infiniband hardware.
> - btl uct is for one-sided but can also be used for two sided as well (needs 
> explicit mca).
> My question is, what if the user does not have UCX installed (but they have 
> infiniband hardware). The user will not have fast transport for their 
> hardware. As of my testing, this release will fall back to btl/tcp if I dont 
> specify the mca to use uct or force openib. Will this be a problem? 

This is a question for Mellanox.

Jeff Squyres

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