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Re: Using -MMD instead of -MD for depndency generation

From: Paul Smith
Subject: Re: Using -MMD instead of -MD for depndency generation
Date: Sun, 31 Oct 2010 13:24:31 -0400

On Thu, 2010-10-28 at 12:18 -0400, Paul Smith wrote:
> > Is there anything I can help with? bisect GNU make 3.81 -> 3.82 to see when 
> > it
> > got slower? Or anything on our GNU make/automake usage? E.g. we use a non
> > recursive makefile
> I'll try to look into this more this afternoon/tonight.  Until then I
> wouldn't bother doing too much work on it.  Let me try to reproduce your
> results then we can see where we are.

I was able to install the proper packages and get a complete build of

After this I see that GNU make 3.82 is twice as slow as 3.81, but even
3.82 only takes about 30 seconds to run (a do-nothing build) on my
system.  Taking 5+ minutes is crazy.  There must be something odd about
your system or setup causing this.

As for why 3.82 is slower, unfortunately I'm having problems figuring it
out.  I compiled with gprof but the cumulative profiled code in GNU make
only took 6 seconds or so, so I suppose the other 24 seconds must be in
libc or someplace... but trying to install a profile-enabled version of
libc on my system did not succeed (or rather the package install worked
but linking with the profiled libc did not work).

All I can assume is there's some difference in heap management in 3.82
which is causing this, because that's the only difference I can think of
that would not show up in the GNU make code itself.  I'll try using
valgrind and see what I get.  If anyone has other suggestions for
profiling tools let me know.


 Paul D. Smith <address@hidden>          Find some GNU make tips at:            
 "Please remain calm...I may be mad, but I am a professional." --Mad Scientist

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