[mpiwg-tools] Open MPI pvar scheme

[Junchao Zhang]

You can think subnames as attached strings to elements in a pvar.
Whether a pvar has subnames or not is optional. So I proposed
MPI_T_pvar_has_subnames()
to query that.

--Junchao Zhang


On Thu, Nov 14, 2013 at 10:57 AM, Jeff Squyres (jsquyres) <
jsquyres at cisco.com> wrote:

> On Nov 13, 2013, at 6:13 PM, Junchao Zhang <jczhang at mcs.anl.gov> wrote:
>
> > Let me comment on the problem in your slides of last teleconf:
> > Slide 2: "Problem: multiple network devices on a server – want to return
> the number of sends on each device but don’t want to create a new variable
> for each of them.
> >   Solution: have each performance variable return an array of values;
> one for each underlying network device"
> >
> > That basically says " (an MPI implementor) creates a multi-element pvar
> (i.e., pvar with count > 1)"
> >
> > Slide 3: "Problem: But how do you know which array slot maps to which
> underlying Linux device?
> >   Solution: the btl_usnic_devices state performance variable."
> >
> > I suppose "YOU"  in the problem is an MPI_T user, for example, a tool
> developer. The question is distilled into "the user wants to know names of
> elements in a multi-element pvar".
>
> We didn't talk about this on the call today.
>
> I don't think I agree with your above statement.  It's not the *name* of
> the pvar that is the issue -- a pvar already has a well-defined name.  It's
> what each element of a pvar value *corresponds to*.  In this case, we have
> a pvar with N elements in its value, and the implementation is
> corresponding each element to a Linux device (and it is desirable for the
> MPI_T user to know what that correspondence is).
>
> We therefore want a way to express that relationship: that each element
> has a string corresponding to it (that is not necessarily a "name" or
> "subname").  However, not all pvars have this kind of relationship.
>
> --
> Jeff Squyres
> jsquyres at cisco.com
> For corporate legal information go to:
> http://www.cisco.com/web/about/doing_business/legal/cri/
>
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