Open MPI logo

Open MPI Development Mailing List Archives

  |   Home   |   Support   |   FAQ   |  

This web mail archive is frozen.

This page is part of a frozen web archive of this mailing list.

You can still navigate around this archive, but know that no new mails have been added to it since July of 2016.

Click here to be taken to the new web archives of this list; it includes all the mails that are in this frozen archive plus all new mails that have been sent to the list since it was migrated to the new archives.

Subject: Re: [OMPI devel] SM init failures
From: Eugene Loh (Eugene.Loh_at_[hidden])
Date: 2009-03-30 14:42:07


Jeff Squyres wrote:

> It's half done, actually. But it was still going to be an option,
> not necessarily the only way to do it:
> http://www.open-mpi.org/hg/hgwebdir.cgi/jsquyres/shm-sysv/
>
> On Mar 30, 2009, at 1:40 PM, Tim Mattox wrote:
>
>> I've been lurking on this conversation, and I am again left with the
>> impression
>> that the underlying shared memory configuration based on sharing a file
>> is flawed. Why not use a System V shared memory segment without a
>> backing file as I described in ticket #1320?
>
In some performance experiments so far, it appears that the start-up
performance of the two approaches are rather different. I don't
understand the results, but I note here that they're different.

Touching all that shared memory upon startup (which, as I noted, we
essentially do now anyhow) adds noticeably to the start-up time. (Less
so now with the single-queue changes. Whether the time is tolerable or
not is a matter of taste, etc.) Going from mmap to SysV speeds that
time up a lot in the tests I've done. But then (mysteriously) the time
to exchange first messages takes much longer.

I'm baffled. For now, I just point out that the performance
characteristics could be different.