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
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