semaphore access speed Post: 302237980

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Top Forums Programming semaphore access speed Post 302237980 by migurus on Thursday 18th of September 2008 09:22:22 PM

09-18-2008

Registered User

I simplified my program to the very basic minimum, it gets ipc key, gets semaphore id and reads values of semaphores and then it outputs on line (time and semaphore values). That is all it does.

Then I run it in following manner:
$ while : ; do tstshow; done > x.txt
and I hit interrupt key after waiting for some time.

sample of the x.txt file content:
1221785538 [1,99]
1221785538 [1,99]
1221785538 [1,99]

Then to see how many times system was able to run it I do:
$ cut -c-12 x.txt | uniq -c

sample of the output:
616 1221785538
615 1221785539
612 1221785540

That tels me the system is capable of running this simple process just roughly 600 times per second.

Just to be consistent I would repeat results here:
PIII under Linux - 900 times/sec
Xeon 3.2 Linux - 600 times/sec
Xeon 3.2 SCO - 1800 times/sec
Systems are idle at the time of test.
How would you explain the results I got? I am trying to find a bottleneck on the modern h/w running Linux.

Please see my new simplified code below:

Code:

 
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <time.h>
#define NSEMS   2
main(int argc, char *argv[])
{
  int           sid;
  ushort        vals[NSEMS] = {0, 0};
        if((sid = semget(get_ipc_key(), NSEMS, 0)) == -1)
        {
                errexit("Can Not Get Semaphore ID");
        }
        if(semctl(sid, NSEMS, GETALL, vals) == -1)
        {
                errexit("Can Not Get Semaphore Values");
        }
        printf("%12li [%i,%i]\n", time(NULL), vals[0], vals[1]);
        exit(0);
}

migurus

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LEARN ABOUT PHP

sem_get

SEM_GET(3)								 1								SEM_GET(3)

sem_get - Get a semaphore id

SYNOPSIS

       resource sem_get (int  $key, [int  $max_acquire = 1], [int  $perm = 0666], [int	$auto_release = 1])

DESCRIPTION

       sem_get(3) returns an id that can be used to access the System V semaphore with the given $key.

	A second call to sem_get(3) for the same key will return a different semaphore identifier, but both identifiers access the same underlying
       semaphore.

PARAMETERS

	      o $key
		-

	      o $max_acquire
		- The number of processes that can acquire the semaphore simultaneously is set to $max_acquire.

	      o $perm
		- The semaphore permissions. Actually this value is set only if the process finds it is the only process currently attached to the
		semaphore.

	      o $auto_release
		- Specifies if the semaphore should be automatically released on request shutdown.

RETURN VALUES

	Returns a positive semaphore identifier on success, or FALSE on error.

CHANGELOG

       +--------+-----------------------------------------+
       |Version |					  |
       |	|					  |
       |	|		Description		  |
       |	|					  |
       +--------+-----------------------------------------+
       | 4.3.0	|					  |
       |	|					  |
       |	|  The $auto_release parameter was added. |
       |	|					  |
       +--------+-----------------------------------------+
NOTES

       Warning

	       When using sem_get(3) to access a semaphore created outside PHP, note that the semaphore must have been created as a set of 3 sema-
	      phores (for example, by specifying 3 as the nsems parameter when calling the C semget() function), otherwise PHP will be	unable	to
	      access the semaphore.

SEE ALSO

       sem_acquire(3), sem_release(3), ftok(3).

PHP Documentation Group 														SEM_GET(3)

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sem_get