[Libreoffice] a faster gnumake ? ...

So,

        Annoyed by the ~12 second incremental do-nothing build-time of writer,
and anticipating the growth of this as we gnu-make-ise the entire build
[ and I appreciate this is better than before but just up-front ;-]. I
did a bit of profiling.

$ time make
[ build ALL ] top level modules: sw
[ build ALL ] loaded modules: sw
[ build CHK ] loaded modules: sw
make: Nothing to be done for `allandcheck'.

real    0m12.604s
user    0m10.347s
sys     0m2.244s

* Thought one:

        Having done an strace - it seems to me that over 2 seconds of that
system time (and I have a fast machine) is consumed simply with stat
syscalls; the attached stat.c does a (typical) stat call 770k times and
it takes me 2 seconds. 97% of our syscalls are 'stats' (770k of them),
and of course they are almost all for the same files.

stats   file
    822 
/data/opt/libreoffice/bootstrap/solver/300/unxlngi6.pro/inc/offuh/com/sun/star/uno/XInterface.hdl
..
    836 /data/opt/libreoffice/bootstrap/solver/300/unxlngi6.pro/inc/comphelper/fileformat.h
..
    876 /data/opt/libreoffice/bootstrap/solver/300/unxlngi6.pro/inc/vcl/dllapi.h
    988 /data/opt/libreoffice/bootstrap/clone/writer/sw/inc/swtypes.hxx
   1307 
/data/opt/libreoffice/bootstrap/solver/300/unxlngi6.pro/workdir/Dep/LinkTarget/Library/libswli.so.d
   1315 
/data/opt/libreoffice/bootstrap/solver/300/unxlngi6.pro/workdir/LinkTarget/Library/libswli.so
   1428 /data/opt/libreoffice/bootstrap/clone/writer/sw/inc/swdllapi.h

http://users.freedesktop.org/~michael/stat-counts.txt - for the full list

        So - the thought is: *why* is gnumake doing this work again and again ?
*surely* we know what output files a make rule touches [ and if we do
not we have problems anyway ], and thus we should know that no files
have changed since last time; can we not assume that and save a ton of
system-calls ?

* Thought two

        Amdahl is not kind to people optimising the 20% instead of the 80%, but
perhaps other silliness is tied to this.        

        Have we done any investigation on what is going on in the guts of make
there ? why is it so paranoid as to stat the same files 1000 times or
so ?

        It'd be nice to know if any further thinking / deeper digging  has gone
on here, before looking myself.

        Thoughts appreciated :-)

                Michael.

-- 
 michael.meeks@novell.com  <><, Pseudo Engineer, itinerant idiot

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <pwd.h>

int doit(void)
{
}

int main (int argc, char **argv)
{
  struct stat st;
  int i;
  for (i = 0; i < 749074; i++) {
    stat 
("/data/opt/libreoffice/bootstrap/solver/300/unxlngi6.pro/workdir/Dep/LinkTarget/Library/libswli.so.d",
 &st);
  }
  return 0;
}