Re: [Automake-NG] [PATCH 1/2] [ng] perf: disable GNU make builtin rules, for performance reasons

[Stefano Lattarini]

On 06/27/2012 07:40 PM, Dave Hart wrote:
> On Wed, Jun 27, 2012 at 17:30 PM, Bob Friesenhahn wrote:
>> On Wed, 27 Jun 2012, Stefano Lattarini wrote:
>>
>>> * lib/am/header-vars (MAKEFLAGS): Append '--no-builtin-rules'.  This
>>> enhance performance by removing GNU make builtin rules that would be
>>> rather irrelevant (e.g., rules to automatically check out files from
>>> from RCS or SCCS repositories), or overridden by Automake (e.g., rules
>>> to compile C or C++ files).  With this simple tweak, the null-build
>>> time on GNU coreutils on an aging Debian system goes down from ~ 20
>>> seconds to ~ 9 seconds.
>>
>>
>> This simple approach seems like a huge improvement.  The improvement will
>> surely be larger if some/all of the files are accessed over a network.
> 
> Yes, good stuff.  Anyone who has debugged Makefiles with GNU make -v
> has seen the insane number of wasted operations due to combinatorial
> explosion exploring possible matches with builtin rules.
> 
> Can Automake be similarly improved to disable GNU make's builtin rules
> without sacraficing compatibility with less-loved make implementations?
>
I think it would be easily doable; it would probably require a configure
time tough (similar to the one that is done to initialize '@SET_MAKE@').
Alas, this would have the side effect or rendering a Makefile created
from a configuration with GNU make early in PATH unusable with non-GNU
makes.  Not a big deal, but an annoyance nonetheless.

Anybody volunteering a patch?

> If it's not practical for Automake to do this for
> all packages, how might a maintainer do it for his package without
> requiring GNU make?
>
He could provide a top-level GNUmakefile containing the

    MAKEFLAGS += --no-builtin-rules

line early, and then including the Automake-generated Makefile:

   include ./Makefile

But that will only clobber the built-in rules for builds launched from
the top-level directory, not from the subdirectories (another good
reason to switch to a non-recursive make setup).

Regards,
  Stefano