Re: parallelization of ./configure compiler test processes

[Zack Weinberg]

On Wed, Mar 29, 2023, at 7:05 PM, Thomas Jahns wrote:
> I spent some time thinking about improvements to autoconf configure
> scripts (while waiting for builds to proceed). In my view, it is
> currently still easier to seek small efficiency gains that, in sum,
> could still improve run-time substantially than parallelizing the
> whole would be, because there is so much often untapped potential:

I do generally agree with this, and I'd also like to remind everyone
that Autoconf has very limited developer resources relative to how
difficult the task of parallelizing _all_ of a configure script will be.

There _are_ some bits of "low hanging fruit" here.  If parallelism
within a configure script is the specific thing what you're interested
in working on, I'd recommend that you start with the macros that check
for a list of things.  We can already say with high confidence that the
four checks done by

    AC_CHECK_HEADERS([a.h b.h c.h d.h])

can be run in parallel, for instance.

> Regarding parallelization for autoconf in particular, I think
> autoconf could very much benefit from having first more explicit
> effects of each macro, i.e. which variables end up being set, which
> file will be appended to etc. To my knowledge this is mostly well
> documented for the human reader, but not programmatically available
> in the M4 phase at all.

This is getting into things that I'm not sure can be done in M4 at
all...

zw