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Subject: Re: [OMPI users] Valgrind writev() errors with 1.3.2.
From: Ralph Castain (rhc_at_[hidden])
Date: 2009-06-09 14:01:10


I can't speak to all of the OMPI code, but I can certainly create a new
configure option --valgrind-friendly that would initialize the OOB comm
buffers and other RTE-related memory to eliminate such warnings.

I would prefer to configure it out rather than adding a bunch of "if-then"
checks for envars to avoid having the performance hit when not needed.

Would that help?

On Tue, Jun 9, 2009 at 11:40 AM, tom fogal <tfogal_at_[hidden]> wrote:

> jody <jody.xha_at_[hidden]> writes:
> > I made a suppression file for the irrelevant memory leaks of ompi: I
> > make no claim that it catches all possible ones, but it catches all
> > that appear in my code.
> [snip]
>
> Thanks, Jody.
>
> What are the chances something like this could be added / maintained in
> the OpenMPI tree? It would be great to have something 1) maintained by
> someone more knowledgeable about these errors than me, and 2) installed
> by default when I setup my toolchain for parallel debugging.
>
> > On Tue, Jun 9, 2009 at 3:28 PM, Jeff Squyres<jsquyres_at_[hidden]> wrote:
> > > This is worth adding to the FAQ.
> > >
> > > On Jun 9, 2009, at 2:31 AM, Ashley Pittman wrote:
> > >
> > >> On Mon, 2009-06-08 at 23:41 -0600, tom fogal wrote:
> > >> > George Bosilca <bosilca_at_[hidden]> writes:
> > >> > > There is a whole page on valgrind web page about this topic.
> Please
> > >> > > read
> > >> > >
> http://valgrind.org/docs/manual/manual-core.html#manual-core.suppress
> > >> > > for more information.
> > >> >
> > >> > Even better, Ralph (et al.) is if we could just make valgrind think
> > >> > this is defined memory. One can do this with client requests:
> > >> >
> > >> >
> http://valgrind.org/docs/manual/mc-manual.html#mc-manual.clientreqs
> > >>
> > >> Using the Valgrind client requests unnecessarily is a very bad idea,
> > >> they are intended for where applications use their own memory
> allocator
> > >> (i.e. replace malloc/free) or are using custom kernel modules or
> > >> hardware which Valgrind doesn't know about.
>
> Okay, sure, I realize it was a bit of an abuse of the intended use of
> the tool.
>
> > >> The correct solution is either to not send un-initialised memory
> > >> or to suppress the error using a suppression file as George
> > >> said. As the error is from MPI_Init() you can safely ignore it
> > >> from a end-user perspective.
>
> As I mentioned in my initial message, MPI_Init is only one such
> error; I get them in a lot of MPI calls, seemingly anything that does
> communication. Though I've heard differently on this list, this led me
> to believe I was doing something wrong in my code.
>
> It seems like the only way I could verify that I'm not causing these
> errors myself is to grok the call stacks I'm given for each vg error
> and figure out where the uninitialized memory comes from, and then make
> a judgement call for myself whether this makes sense to suppress. Or
> I could mail the list about every error I see and ask for confirmation
> that it's benign/suppressable. Most likely, I'll take the simple
> approach and just use the suppression file I was given, but that's
> prone to be fragile and break with a future OpenMPI release.
>
> What about an environment variable which enables slower,
> valgrind-friendly behavior? There's precedent in other libraries, e.g.
> glib [1].
>
> -tom
>
> [1] http://library.gnome.org/devel/glib/stable/glib-running.html
>
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