On Monday 16 October 2006 22:37, Al Viro wrote:
> FWIW, that reminds me - I ought to resurrect the
> patchset killing bogus dependencies; I modified sparse to collect stats
> on how many times each #include actually pulls a header during build,
> added those to data on dependencies (from .cmd.*) and got interesting
> results.
are these modifications publically available? i would be interested to see
them. i've been grovelling over the header files with perl...
> There are several #includes with very high impact; the worst happens
> to be module.h -> sched.h, followed by several includes of fs.h. These
> turned out to be easy to kill (i.e. few places actually needed compensatory
> #include added) and that had seriously cut down on total dependencies.
> The patches will need to be redone due to bitrot, but they are not
> hard to reproduce. The really interesting observation is that such
> high-impact includes exist and can be found by this technics...
i noticed another potential source of unneccessary dependencies:
<linux/prefetch.h> includes <asm/processor.h> for a total of ~49
dependencies. it appears that the prefetch() concept could be moved into a
separate <asm/prefetch.h> file with much smaller dependency footprint, for a
pretty hefty reduction in total dependencies throughout the system.
another potential win: a good chunk of <linux/kernel.h> (which has ~24
dependencies) actually has nothing to do with the kernel per se. i'm
thinking of basic C language idioms (container_of(), typecheck(), etc) and
constants (INT_MAX). a fair number of files seem to include <linux/kernel.h>
just for these items. moving that stuff into a separate file (<linux/c.h>?)
could eliminate 20 or more bogus deps from many locations.
ray
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