During the Christmas holidays in 1989, I ran a little benchmark
(`forktime') on various machines. The program was roughly
loop many times
fork
parent waits
child exits
I ran it twice or more linked statically and twice or more linked
dynamically on each machine. The machines were lightly loaded. For
1000 iterations, user time is consistently about 100ms for
statically-linked forktime, but 4-11 times that when dynamically
linked (i.e., using shared libraries).
System times are more interesting. SunOS 3.5 had no shared libraries,
so Sun seems to have sped up fork() by about 50% between SunOS 3.5 and
4.0 for statically-linked programs, but then lost all that performance
and more when using shared libraries on 4.0, which took almost 4 times
as much system time as statically-linked forktime on 4.0.
We scratched our heads about what in the world the kernel was doing
for 42ms per fork. Even on a Sun 3/50, that's a lot of cycles.
This was a long time ago, but it's some actual measurements.
--- fork times ---
: utubrutus; time ./forktime 1000 # sun 3/50 sunos 3.5 diskless
22.9 real 0.1 user 22.0 sys
22.6 real 0.1 user 22.1 sys
: nil.ai; time 3s/forktime 1000 # sun 3/50 sunos 4.0 diskless -Bstatic
12.0 real 0.1 user 11.7 sys
11.9 real 0.1 user 11.7 sys
: nil.ai; time 3/forktime 1000 # sun 3/50 sunos 4.0 diskless dynamic
46.8 real 0.8 user 41.7 sys
46.9 real 1.1 user 42.4 sys
45.9 real 0.9 user 42.2 sys
: neat.cs; time 4s/forktime 1000 # sun 4/280 sunos 4.0 -Bstatic
12.7 real 0.1 user 11.8 sys
12.0 real 0.1 user 11.2 sys
: neat.cs; time 4/forktime 1000 # sun 4/280 sunos 4.0 dynamic
29.9 real 0.4 user 25.3 sys
35.4 real 0.5 user 25.0 sys
---
/*
* forktime - execute many forks for timing
*/
#define NULL 0
/* imports */
long atol();
main(argc, argv)
int argc;
char **argv;
{
register long count = 1000;
if (argc > 1)
count = atol(argv[1]);
while (count-- > 0) {
register int pid = fork();
if (pid < 0)
perror(argv[0]);
else if (pid == 0) /* child */
_exit(0);
else {
register int deadpid;
while ((deadpid = wait((int *)NULL)) != pid && deadpid
!= -1)
;
}
}
_exit(0);
}
