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Subject: Re: [OMPI devel] Using external libevent
From: Orion Poplawski (orion_at_[hidden])
Date: 2013-04-27 22:37:14


On 04/26/2013 08:53 PM, Ralph Castain wrote:
>
> On Apr 26, 2013, at 7:40 PM, Orion Poplawski <orion_at_[hidden]> wrote:
>
>> 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)
>
> Just for clarification: who or what is "spot"?

Tom "spot" Callaway - one the packaging committee members

>>
>> 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.
>
> As I said, I'll take a look at it, but can't commit to having it available any time soon. It isn't something I would suggest someone try who isn't fully versed in OMPI's code base.

Yeah, I'm not looking forward to it. I get to at least wait until the
non-threaded version of libevent is available.

-- 
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