Re: Compiling large number of files

[Bob Friesenhahn]

On Wed, 6 Oct 2004, v p wrote:

> Hi Guys,
> I have a question. I am using autotools to build my static library.
> The way I do it is, I have a Makefile.am as
> lib_LIBRARIES = libmylib.a
> libmylib_a_SOURCES = xyz.c abc.c etc.
>
> The problem is the number of source files is huge (1659 files to be
> precise) and that's why it takes a lot of time to compile all this.
> When I run the generated makefile, I see 'gcc' being invoked for each
> of the source files. Loading 'gcc' into memory for each file is a time
> consuming process, and it is possible to compile more than one file at
> a time using gcc. If I could make generated makefile do this, my build
> process will be much faster. Is there any way to achieve this using
> Makefile.am and automake.

I suggest that you do some testing by hand to see what performance 
benefit is really gained from passing multiple source files to gcc.

Most modern Unix systems are exceedingly fast at starting large 
programs like GCC and once it has been executed once, the executables 
and libraries are actually cached in RAM so subsequent executions are 
faster.  Here is an example:

% time gcc --version > /dev/null
gcc --version > /dev/null  0.00s user 0.00s system 0% cpu 0.004 total

If builds are much slower using Automake, the problem is most likely 
that the scripting associated with automatic dependency generation is 
slowing down the build.  You can configure with 
--disable-dependency-tracking but then you won't have dependency 
information (which developers normally need).

Bob
======================================
Bob Friesenhahn
address@hidden
http://www.simplesystems.org/users/bfriesen