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Full Discussion: AIX - io info get from "libperfstat" not match "iostat"
Top Forums UNIX for Advanced & Expert Users AIX - io info get from "libperfstat" not match "iostat" Post 302903678 by jackliang on Thursday 29th of May 2014 01:35:21 AM
Old 05-29-2014
AIX - io info get from "libperfstat" not match "iostat"
Hi, everyone.
I need to write a program to get io info based on libperfstat.
But the "write time" of a disk is just half of the value get from iostat.
I'm confused and can't explain. Help please.

How I calculate "write service time per sec":

In iostat:
Code:
 
        write service time per sec = wps * avgserv
        wps: write requests per sec
        avgserv: avg service time per write request

In my program:
Code:
        (new wserv - old wserv) / intervalTime

iostat cmd:
Code:
 iostat -D hdisk1 10

My C code :
Code:
    int i, ret, tot;
    perfstat_disk_t *statp;
    perfstat_id_t first;
    
    unsigned long long oldValue = 0;
    unsigned long long newValue = 0;
    int interval = 10;
    
    while (true) {
        /* check how many perfstat_disk_t structures are available */
        tot =  perfstat_disk(NULL, NULL, sizeof(perfstat_disk_t), 0);
    
        /* allocate enough memory for all the structures */
        statp = calloc(tot, sizeof(perfstat_disk_t));
    
        /* set name to first interface */
        strcpy(first.name, FIRST_DISK);
    
        /* ask to get all the structures available in one call */
        /* return code is number of structures returned */
        ret = perfstat_disk(&first, statp,
            sizeof(perfstat_disk_t), tot);
    
        /* print statistics for each of the disks */
        for (i = 0; i < ret; i++) {
            if (strcmp(statp[i].name, "hdisk1") == 0) {
                printf("\nStatistics for disk : %s\n", statp[i].name);
                printf("-------------------\n");
                newValue = statp[i].wserv;
                printf("write time : %llu /s\n", (newValue - oldValue)/interval);
                oldValue = newValue;
            }
        }
    
        sleep(interval); // sleep 10s
    }

 

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LEARN ABOUT OSF1

iostat

iostat(1)						      General Commands Manual							 iostat(1)

NAME

       iostat - Reports I/O statistics

SYNOPSIS

       iostat [drive...] [interval] [count]

OPERANDS

       Forces  iostat  to  display  specific  drives.	If drive is not specified (or the specified drive does not exist on the system or cluster,
       iostat displays the first two drives (even if more than two disk drives are configured in the system).  Causes iostat to report	once  each
       interval  seconds.   The first report is for all time since the system was last booted, and each subsequent report is for the last interval
       only.The value must not be 0.  Specifies the number of reports.	For example, iostat 1 10 would produce 10 reports at  1-second	intervals.
       You cannot specify count without interval because the first numeric argument to iostat is assumed to be interval.

DESCRIPTION

       The  iostat  command reports the following information: For terminals (collectively), the number of characters read and written per second.
       For each disk, the number of transfers per second and bytes transferred per second (in kilobytes).  For the system, the percentage of  time
       the system has spent in user mode, in user mode running low priority (nice) processes, in system mode, and idling.

       To  compute  this  information,	iostat counts data transfer completions, the number of words transferred for each disk, and the collective
       number of input and output characters for terminals. Also, each sixtieth of a second, iostat examines the state of each disk  and  makes  a
       tally if the disk is active.

       When  you  issue  an  iostat command on a cluster member, it displays statistics only for those disks that are local to the member and that
       member's usage of those shared disks that it has mounted.   It displays 0 for other disks in the cluster (those it doesn't  have  mounted),
       regardless of whether they are on the shared bus or are local to some other member.

EXAMPLES

       The  output  from  this	example displays cpu, terminal, and disk statistics for the first two disks on the system providing 5 reports at 1
       second intervals:

       # iostat 1 5
	   tty	    floppy1	     dsk9	   cpu
	tin tout    bps    tps	  bps	 tps  us ni sy id
	  0    3      0      0	    0	   0   1  0  4 95
	  4   58      0      0	    0	   0   1  0  2 97
	  1   53      0      0	    0	   0   0  0  2 98
	  5   59      0      0	    0	   0   1  0  1 98
	  6   60      0      0	    0	   0   1  0  2 97

       The second example specifies device names in the command:

       # iostat dsk2 dsk3 cdrom2
	      tty	dsk2	cdrom2	     dsk3	  cpu
	tin   tout  bps  tps  bps  tps	 bps  tps  us  ni  sy  id
	  0    13    11   5    5    2	2427 1213   0	1   1  98

SEE ALSO

       Commands:vmstat(1)

																	 iostat(1)
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