Re: Autoconf 2.63b test release

[Eric Blake]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

According to Robert Schwebel on 3/31/2009 7:13 AM:
> On Tue, Mar 31, 2009 at 06:37:45AM -0600, Eric Blake wrote:
>> Highlights (in no particular order): Configure scripts are now built using
>> shell functions, which leads to much smaller configure scripts.  Execution
>> time of both autoconf and built configure scripts have been improved.
>> Autotest added an experimental feature for parallel testsuite execution.
>> AC_REQUIRE has been made smarter, and fixed an out-of-order expansion bug
>> that had been present for more than 8 years.  See the NEWS excerpt below
>> for more details, and a couple of things to note when upgrading.
> 
> How is this supposed to be used? This is a simple hello world program:
> 
> address@hidden:tmp$ ls -l test-2.61/configure test-2.63b/configure
> -rwxr-xr-x 1 rsc rsc 741280 Mar 31 15:00 test-2.61/configure
> -rwxr-xr-x 1 rsc rsc 705596 Mar 31 15:02 test-2.63b/configure
> 
> -> 5% size reduction

The more macros you invoke (particularly of the AC_COMPILE_IFELSE
variety), the better the size reduction.  GNU Coreutils dropped from over
2 megabytes down to 1, almost 50% smaller.

> 
> time (./configure && make) -> real 7.93 s (with 2.61)
>                                    7.39 s (with 2.63a)

Here, you're mixing configure timing with make timing, rather than timing
configure in isolation; but your numbers did show a speedup.  Make is not
going to be any faster due to autoconf changes (although you may want to
look at automake 1.10b, also released this week, which does improve things
like 'make install' speed).  Again, the more macros your configure.ac
invokes, the faster autoconf 2.63b will create configure in relation to
how autoconf 2.63 performed.  In turn, the configure script will run
faster (easily 50% faster on platforms like cygwin where forks are
expensive, but even on Linux I have seen at least 10% faster configure
performance).

> 
> Do I have to do something special to get the better execution time?

No.  For simple projects, you won't see as much improvement, because there
is simply less opportunity to reduce file size and forks when there are
fewer tests to begin with.  What is more important is that as your project
grows to a larger scale, the improvements provided by newer autotools
become even more apparent over the speed provided by previous versions.

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (Cygwin)
Comment: Public key at home.comcast.net/~ericblake/eblake.gpg
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iEYEARECAAYFAknSLcUACgkQ84KuGfSFAYB2/ACfVSMscYty6ek6W6mft3sfyeYG
aucAoKWk8NHKhLd7bDqwwAAtPr8w5HdF
=I0Ql
-----END PGP SIGNATURE-----