[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

Re: OpenMPI 5.0 to be 32-bit only ?

On Mon, Feb 13, 2023 at 02:18:06PM +0000, Alastair McKinstry wrote:

> On 13/02/2023 12:51, Adrian Bunk wrote:
> > On Mon, Feb 13, 2023 at 10:59:18AM +0000, Alastair McKinstry wrote:
> > > ...
> > > > The case we should make is that "no one cares about 32-bit builds" from
> > > > the starting post in the GitHub issue is not true for Debian.
> > > > We do care that it *builds*, even if it might not be actually used.
> > > I've been making this point, mostly in the context of avoiding a future
> > > where no MPI is available on 32-bit
> > > (and by implication, essentially forking Debian into a toy 32-bit world and
> > > a properly-supported 64-bit one).
> > I don't see what important functionality for 32-bit today would be
> > missing without MPI, it is just more work and breakages to have packages
> > configured differently on different platforms to continue providing the
> > functionality that is still important.

> There are a significant number of science libraries dependent on MPI.

> We would need to do MPI-free builds of these libraries; I'm not sure how
> much breaks as we do.

Would we, though?  Or should we remove the 32-bit builds of those libraries
as well?

I think it's accurate that no one is using those scientific libraries in
production (which is, basically: doing lots of matrix math) on 32-bit
architectures, because all of the vector instructions you want for such work
are only available on 64-bit CPUs.

So the only application of those 32-bit binaries, really, is either a)
letting users of those 32-bit archs learn the tools on the hardware they
have available, so they can use them to advantage later on fit-for-purpose
hardware; or b) using them to build other software in Debian.

Is either of those a compelling reason to keep building those software
stacks for 32-bit?  I would argue not.  But neither is it obvious at what
point it's worth the effort to remove them, since this requires tracking the
reverse-dependency tree, working out which of those reverse-dependencies are
*not* scientific applications that should drop the build-dependency rather
than being removed, and so forth.

So it's a tradeoff between the maintenance work of keeping mpi working on
32-bit, and the one-time work of removing it.

> > > ...
> > > The point of going  64-bit only is to clean up data structures and remove
> > > technical debt: Hence 5.x will start a cleanup and removal of 32-bit code.
> > > 
> > > The next point release may work on 32-bit by just bypassing the
> > > compilation flag; ongoing support starts meaning more invasive patches
> > > need to be carried by us.

Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                   https://www.debian.org/
slangasek@ubuntu.com                                     vorlon@debian.org

Attachment: signature.asc
Description: PGP signature

Reply to: