From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Brannon <cmbrannon@cox.net>
To: 9fans@9fans.net
Date: Fri, 20 Feb 2009 13:35:07 -0600
Message-Id: <20090220193401.KHHY16134.fed1rmmtao104.cox.net@fed1rmimpo03.cox.net>
Subject: [9fans] impact of dynamic libraries on the speed of fork()
Topicbox-Message-UUID: a4b915e6-ead4-11e9-9d60-3106f5b1d025

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

--- begin transcript ---
Script started on Fri 20 Feb 2009 01:23:10 PM CST
% dietcc forktest.c # link statically against dietlibc
% ./a.out
30864.1 forks per second
% gcc forktest.c # compile with gcc, dynamic linking
% ./a.out
15723.3 forks per second
% gcc forktest.c -lm # pull in the math library
% ./a.out
14792.9 forks per second
% gcc forktest.c -lm -lcurses
% ./a.out
13888.9 forks per second
% gcc forktest.c -lm -lcurses -lpthread
% ./a.out
11961.7 forks per second
% . gcc forktest.c -lm -lcurses -lpthread -lresolv
% ./a.out
11013.2 forks per second
% gcc forktest.c -lm -lcurses -lpthread -lresolv -lssl
% ./a.out
8250.83 forks per second
% gcc forktest.c -lm -lcurses -lpthread -lresolv -lssl -lreadline
% ./a.out
7961.78 forks per second
% exit

Script done on Fri 20 Feb 2009 01:27:20 PM CST
--- end transcript ---

---begin forktest.c---
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

int
main(void)
{
    double elapsed_secs;
    int forks = 0;
    clock_t start = clock(), elapsed;
    int i;
    for(i = 0; i < 25000; i++) {
	int waitstatus;
	switch (fork()) {
	case -1:
	    perror("fork");
	    break;
	case 0:
	    exit(42);
	default:
	    wait(&waitstatus);
	    ++forks;
	    break;
	}
    }
    elapsed = clock() - start;
    elapsed_secs = (double)elapsed / CLOCKS_PER_SEC;
    printf("%g forks per second\n", (double)forks / elapsed_secs);
    exit(0);
}
---end forktest.c---