Re: build system rules & algorithms

[Eli Zaretskii]

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> Date: Thu, 11 Jun 2009 22:27:48 -0400
> From: Mike Shal <address@hidden>
> Cc: address@hidden
> 
> On 6/11/09, grischka <address@hidden> wrote:
> > Mike Shal wrote:
> >
> >
> > > For some hard numbers, my
> > > machine takes 17s to run make in an already-built linux kernel tree.
> > > Just doing a 'find . | xargs stat > /dev/null' only takes 2.6s though,
> > > so I would guess the remaining ~14s are mostly for parsing Makefiles
> > > and processing the DAG.
> > >
> >
> >  Careful with conclusions from "hard numbers".
> 
> Fair point :)
> 
> >
> >  Consider that in comparison to "17s to run make in an already-built linux
> >  kernel tree", TCC needs ~15 seconds to COMPILE AND LINK the entire linux
> >  kernel tree -> http://bellard.org/tcc/tccboot.html.  That
> > at least shows
> >  that no program would spend that "~14s" just to read some Makefiles or
> >  loop over some linked lists (i.e. "processing the DAG").
> 
> I've never heard of TCC - I'll have to check it out! Though my point
> was merely that make is doing *something* during those 17s, none of
> which is useful to me since no files have actually changed in the
> kernel tree. The stat()ing is just a rough estimate of that portion of
> make's execution time. Is there a better way to benchmark it to figure
> out the bottlenecks?
> 
> >  After all GNU make is not "the reference implementation of an alpha build
> >  system".  It is a piece of code with a long history with more going on
> >  than just a few O(n) lookups.  You might find features like checkout
> >  from RCS/SCCS version control via built-in rules which is obsolete stuff
> >  since long ago, still everyone using GNU make today is paying for it with
> >  maybe 80% of it's total CPU time, worldwide. (Try "make -r ..." to see
> >  what I mean).
> 
> Yeah, I've seen some pages that document how to get rid of a bunch of
> that built-in stuff (there were a few patterns you had to add to a
> Makefile as well, if I recall correctly). Has anyone done benchmarks
> on that to see what kind of overhead that actually accounts for?
> 
> >  Anyway, good luck with TUP, I'll try it out.  And waiting for your new
> >  "beta CONFIGURE system", if any possible one that doesn't rely on
> >  megabytes of unmaintainable shell scripts ... ;)
> 
> Thanks! I might want to leave the configure system to someone else, though :)
> 
> -Mike
> 
> 
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