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Subject: Re: [OMPI devel] OpenMPI Performance Problem with Open|SpeedShop
From: George Bosilca (bosilca_at_[hidden])
Date: 2009-01-12 14:08:28

There might be one reason to slowdown the application quite a bit. If
the fact that you're using timer interact with the libevent (the
library we're using to internally manage any kind of events), then we
might end-up in the situation where we call the poll for every
iteration in the event library. And this is really expensive.

A quick way to figure out if this is that case is to run Open MPI
without support for shared memory (--mca btl ^sm). This way we will
call poll on a regular basis anyway, and if there is no difference
between a normal run and a OSS one, we know at least where to start
looking ...


On Jan 12, 2009, at 13:00 , Jeff Squyres wrote:

> On Jan 9, 2009, at 12:39 AM, William Hachfeld wrote:
>> Can any of the OpenMPI developers speculate as to possible
>> mechanisms by which the ptrace() attachment , signal handler, or
>> timer registration and corresponding signal delivery could cause
>> large amounts of time to be spent within the "progress" functions
>> of the OpenMPI library with an apparent lack of any real progress?
>> Any ideas/information would be greatly appreciated.
> Hum; interesting. I can't think of any reason why that would be a
> problem offhand. The mca_btl_sm_component_progress() function is
> the shared memory progression function. opal_progress() and
> mca_bml_r2_progress() are likely mainly dispatching off to this
> function.
> Does OSS interfere with shared memory between processes in any way?
> (I'm not enough of a kernel guy to know what the ramifications of
> ptrace and whatnot are)
> --
> Jeff Squyres
> Cisco Systems
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