Subject: Re: [bug#27905] changes for openmpi

From: Dave Love <[email-masked]>
Date: Fri, 01 Sep 2017 12:06:14 +0100

Ludovic Courtès <[email-masked]> writes:

>> * mpi.scm (hwloc)[outputs]: Replace lib with nogui.
>> (hwloc)[arguments]: Change configure --prefix; use "nogui" output,
>> not "lib"; populate "all" output.
>> (openmpi)[inputs]: Use hwloc-nogui.
>
> The downside of this is that the “nogui” output is less discoverable
> (and it’s another user-visible breakage.)

I don't understand why it's worse than currently.  "hwloc" will provide
the same as before, won't it?  I guess developer breakage could be fixed
by retaining the lib output if it matters.

Maybe it's helpful to try to document what sort of stability is expected
currently?

> Also, it shouldn’t make any difference to the closure size of openmpi
> anyway, no?

Right.  It wasn't for openmpi specifically.

>> +         (add-after 'install 'install-openmpi
>> +           (lambda* (#:key outputs #:allow-other-keys)
>> +             (let ((dest (format #f "~a/lib/valgrind"
>> +                                 (assoc-ref outputs "openmpi"))))
>> +               (mkdir-p dest)
>> +               (zero?
>> +                (system (format #f "mv ~a/lib/valgrind/libmpiwrap* ~a"
>> +                                (assoc-ref outputs "out") dest)))))))))
>
> Why move it to a separate output?  After all, we can keep it in “out”
> since all it costs is the size of libmpiwrap.so, right?
>
> Also, I assume that this is functionally equivalent to Open MPI’s
> built-in Valgrind support, is it?

This is probably moot.  It isn't entirely equivalent but, more
importantly, the builtin support apparently doesn't have the performance
hit which was documented; I haven't checked experimentally.  See this
thread, though not all my questions were answered:
<https://www.mail-archive.com/[email-masked]//msg31459.html>.

The wrapper library may still be relevant for mpich-y MPIs, if they get
used -- I don't know.