Re: [9fans] impact of dynamic libraries on the speed of fork()

[erik quanstrom <quanstro@quanstro.net>]

On Fri Feb 20 14:35:45 EST 2009, cmbrannon@cox.net wrote:
> I wrote a really simple program, forktest.c.
> Next, I performed some experiments using this program.  Fork is faster
> for statically linked executables.  It becomes slower as more libraries
> are added to a dynamically linked executable.
> These tests were done on an x86 machine running Linux.
> Here is a transcript of my experiments, followed by the source for forktest.
>
> -- Chris

very nice.

i wonder if you may be measuring the performance
of memory management more than the performance of dynamic
linking.  the reason i suspect this is because on my p3 machine i see

gcc static	13440 f/s
gcc dyn	12953 f/s
gcc static 6963 fork + exec/s

or the tipoff is the size of the executable:

; ls -l a.out
-rwxr-xr-x 1 quanstro users 609298 Feb 20 14:36 a.out

for snarky comparison, here are the programs on my system that
are that large or larger:
--rwxrwxr-x M 48625 sys      sys    13275174 Jan 16  2006 /bin/gs
--rwxrwxr-x M 48625 sys      sys      758520 Dec  9  2005 /bin/spin

the hard bit would be keeping the memory footprint the
same while increasing the number of shared libraries.

even in bad cases, this is like 0.2ms/fork + exec.
i wonder if the reason that there can be such big
differences is that linux fork+exec may have been
massaged for such syntetic benchmarks.  thus small
amounts of extra work might look big.

- erik