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Subject: Re: [OMPI devel] Using external libevent
From: Orion Poplawski (orion_at_[hidden])
Date: 2013-04-26 22:40:15


On 04/25/2013 04:48 AM, Jeff Squyres (jsquyres) wrote:
> Orion --
>
> I would just caution against using Open MPI with a thread-enabled libevent. In most cases, the performance impact wouldn't matter, but the whole point of MPI is to be high performance. The current 1.7 series does *not* use a thread-enabled libevent because it detracts from performance. Hence, using a thread-enabled libevent detracts from Open MPI's main purpose.
>
> If Open MPI is suddenly bundled with a thread-enabled libevent, *performance will go down* and users will be unhappy. We have learned painfully over the years that users expect good performance out of the box -- if they have get "bad" performance out of the box and have to do something special to enable "good" performance, they'll be annoyed and blame Open MPI.
>
> So I would request that you do *not* link Open MPI against a thread-enabled libevent until we are able integrate such functionality properly, and take measures to mitigate the performance implications (which likely won't be until at least the 1.9 series).

So, the Fedora Packaging committee has taken that part to heart, but not
the bundling:

* Bundling exception for libevent in openmpi -
   https://fedorahosted.org/fpc/ticket/273 (spot, 16:16:52)
   * ACTION: FPC is pretty universally against this bundling, spot will
     try to make a libevent-nothread.so and update libevent. (spot,
     16:26:38)

So it looks like I will need to shortly be looking at how to link
against an external libevent. Any help with that would be greatly
appreciated.

-- 
Orion Poplawski
Technical Manager                     303-415-9701 x222
NWRA/CoRA Division                    FAX: 303-415-9702
3380 Mitchell Lane                  orion_at_[hidden]
Boulder, CO 80301              http://www.cora.nwra.com