Re: Announcing Dolt, a drop-in Libtool replacement which cuts build times in half

[Bob Friesenhahn]

On Wed, 9 Apr 2008, Eric Blake wrote:
> | Since shell scripts are not compiled, the size of a shell script has
> | very little to do with its execution time.
>
> On the other hand, recent improvements in autoconf 2.62 proved that we
> were able to speed up testsuite performance by more than 10% by merely
> refactoring Autotest output to avoid shell parsing of code that would not
> be executed.  In other words, the time the shell spends on parsing its
> input, whether or not that input is executed, is not trivial.

This is true.  The script could be 10MB in size but if only the first 
five lines are ever executed the execution time should be similar to a 
similar five line script.  This means that parts which are executed 
often should be up front.

If there is a long list of shell functions which appear up front, then 
all those shell functions need to be parsed and remembered before the 
real executable code is executed.

There may be value to extracting these shell functions into separate 
files which are sourced only when needed.  This way the overhead of 
parsing "linking" code is not encountered while compiling, and 
vice-versa.  Since there is surely overhead associated with opening 
and sourcing a file the chunk of code should be pretty large.

Unfortunately, more files gives people more to complain about since a 
single large file is less offensive than many smaller files.

If the build-time overhead associated with libtool 2.2 (vs Dolt) is 
really only 13% or so, someone needs to make the call as to what is an 
acceptable level of runtime overhead before Dolt can be disposed of an 
unecessary idea.  Is the acceptable overhead 5%, 7%, 10%?  What is the 
magic number?

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