Re: Non-recursive makefiles, and static pattern rules

[Alejandro Colomar <alx@kernel.org>]

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> Date: 2026-10-07 22:07:46+0200
> From: Alejandro Colomar <alx@kernel.org>
>
> Hi Miguel,
> 
> 
> As we talked earlier today, if you're trying to improve performance of
> the kernel makefiles, I recommend checking a few things we've done in
> the man-pages.git repo.
> 
> In the man-pages, we have a huge set of makefiles (not as large as the
> kernel, but 120k is already huge for the scale of this project).  The
> performance seems nice, and it's a non-recursive set of makefiles.
> 
> (If you're curious, the reason we have so much makefile code is that
>  I set up a large number of linters to run in the build system, with
>  'make -R lint'.  See 'make -R help' and 'make -R help-targets' if you

Oops, it's s/help-targets/help-list-targets/


Cheers,
Alex

>  want to look at what we have available there.)
> 
> We use static pattern rules:
> <https://www.gnu.org/software/make/manual/html_node/Static-Pattern.html>
> 
> That is:
> 
> 	targets …: target-pattern: prereq-patterns …
> 		recipe
> 		…
> 
> This results in a huge database when make(1) runs, being 10x larger than
> what we would get with regular pattern rules.
> 
> However, recently I tried moving to pattern rules, since I thought the
> smaller database could improve performace, but the experience was
> surprising: the run time degraded by several orders of magnitude.
> I don't remember the exact numbers, but a full
> 	'make -R -j24 build-all lint check'
> (which is building almost everything that the build system can build)
> would take a few minutes with the huge database, and several hours with
> the size-optimized database using regular pattern rules.
> 
> I suspect it's because by having to guess for each file which rule to
> apply (and being non-recursive, it has the whole list of thousands of
> files, and around a hundred different patterns, so the combination is
> explosive) is too expensive.  By using pattern rules, make(1) doens't
> have to guess, and thus goes directly to the rule that applies to each
> file.
> 
> I think this might solve the issues you were seeing in your experiment.
> (Or it might not.)  :-)
> 
> Please let me know if this changes anything in your experiments!
> 
> 
> Have a lovely night!
> Alex
> 
> 
> -- 
> <https://www.alejandro-colomar.es>



-- 
<https://www.alejandro-colomar.es>

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