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Full Discussion: semaphore access speed
Top Forums Programming semaphore access speed Post 302243597 by otheus on Monday 6th of October 2008 05:57:28 AM
Old 10-06-2008
Migurus,

I emailed the maintainers of the code. This is a response I got back from Alan "Maddog" Cox (with permission to post here):
Quote:
Quote:
Perhaps you can contribute to this discussion (concerning SCO vs linux performance differences with semget):
No but if you've got a good test case using gettimeofday() rather than time
so you get high precision time data file a bug in bugzilla.kernel.org as I
imagine Ingo Molnar and a few others might be interested.

High performance Linux code uses futex locks rather than sys5 locks but it
would still be nice to know if there really is such a big difference and why

Alan
So here is yet another version using gettimeofday(). Don't bother posting the benchmarks here, unless they are significantly different. But prepare them for bugzilla:
Code:
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <time.h>
#define NSEMS   2

const static long maxseconds = 1000;
main(int argc, char *argv[])
{
    struct timeval tod_start,tod_stop;
    long int start,stop;
    long int maxloop = 5000000;
    long int i;
    int sid;
    key_t key;
    ushort vals[NSEMS] = { 0, 0 };

    if (argc > 1)
      maxloop = atol(argv[1]);
    i = maxloop;

    key = ftok("/tmp",99);

    gettimeofday(&tod_start, NULL);
    while (--i) {
      if ((sid = semget(key, NSEMS, IPC_CREAT | 0777)) == -1) {
          perror("Can Not Get Semaphore ID");
      }
      if (semctl(sid, NSEMS, GETALL, vals) == -1) {
          perror("Can Not Get Semaphore Values");
      }
    }
    gettimeofday(&tod_stop,NULL);

    start = 1000*1000*(tod_start.tv_sec - maxseconds) + tod_start.tv_usec;
    stop  = 1000*1000*(tod_stop.tv_sec  - maxseconds) + tod_stop.tv_usec;

    printf("%.2f semop/s (%ld/%ld)\n",
      (double)maxloop/(stop-start)*1000*1000, maxloop, stop-start);
}

 

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LEARN ABOUT OPENSOLARIS

settimeofday

gettimeofday(3UCB)				     SunOS/BSD Compatibility Library Functions					gettimeofday(3UCB)

NAME

       gettimeofday, settimeofday - get or set the date and time

SYNOPSIS

       /usr/ucb/cc [ flag ... ] file ...
       #include <sys/time.h>

       int gettimeofday(tp, tzp)
       struct timeval *tzp;
       struct timezone *tzp;

       int settimeofday(tp, tzp)
       struct timeval *tzp;
       struct timezone *tzp;

DESCRIPTION

       The  system's notion of the current Greenwich time is obtained with the gettimeofday() call, and set with the settimeofday() call. The cur-
       rent time is expressed in elapsed seconds and microseconds since 00:00 GMT, January 1, 1970 (zero hour). The resolution of the system clock
       is hardware dependent; the time may be updated continuously, or in clock ticks.

	 long tv_sec;	   /* seconds since Jan. 1, 1970 */
	 long tv_usec;	     /* and microseconds */

       tp points to a timeval structure, which includes the following members:

       If tp is a NULL pointer, the current time information is not returned or set.

       tzp is an obsolete pointer formerly used to get and set timezone information. tzp is now ignored. Timezone information is now handled using
       the TZ environment variable; see TIMEZONE(4).

       Only the privileged user may set the time of day.

RETURN VALUES

       A -1 return value indicates an error occurred; in this case an error code is stored in the global variable errno.

ERRORS

       The following error codes may be set in errno:

       EINVAL	 tp specifies an invalid time.

       EPERM	 A user other than the privileged user attempted to set the time.

SEE ALSO

       cc(1B), adjtime(2), ctime(3C), gettimeofday(3C), TIMEZONE(4)

NOTES

       Use of these interfaces should be restricted to only applications written on BSD platforms.  Use of these interfaces with any of the system
       libraries or in multi-thread applications is unsupported.

       tzp is ignored in SunOS 5.X releases.

       tv_usec is always 0.

SunOS 5.11							    30 Oct 2007 						gettimeofday(3UCB)
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