progconc/syscall_speed.c

This is progconc/syscall_speed.c, an example to accompany the book, The Linux Programming Interface.

This file is not printed in the book; it is a supplementary file for Chapter 3.

In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

Download progconc/syscall_speed.c

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Function list (Bold in this list means a function is not static)

main()

/* syscall_speed.c

   By repeatedly invoking a simple system call (getppid()), we can get some
   idea of the cost of making system calls.

   Usage: time syscall_speed numcalls
                           Def=10000000

   Compiling with -DNOSYSCALL causes a call to a simple function
   returning an integer, which can be used to compare the overhead
   of a simple function call against that of a system call.
*/
#include "tlpi_hdr.h"

#ifdef NOSYSCALL
static int myfunc() { return 1; }
#endif

int
main(int argc, char *argv[])
{
    int numCalls = (argc > 1) ? getInt(argv[1], GN_GT_0, "num-calls")
                              : 10000000;

#ifdef NOSYSCALL
        printf("Calling normal function\n");
#else
        printf("Calling getppid()\n");
#endif

    for (int j = 0; j < numCalls; j++)
#ifdef NOSYSCALL
        myfunc();
#else
        getppid();
#endif

    exit(EXIT_SUCCESS);
}

Download progconc/syscall_speed.c

Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.