Re: build system rules & algorithms

[grischka]

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".

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").

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from RCS/SCCS version control via built-in rules which is obsolete stuff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).

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 ... ;)

--- grischka