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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 NETBSD

iostat

IOSTAT(8)						    BSD System Manager's Manual 						 IOSTAT(8)

NAME

     iostat -- report I/O statistics

SYNOPSIS

     iostat [-CdDITx] [-c count] [-M core] [-N system] [-w wait] [drives]

DESCRIPTION

     iostat displays kernel I/O statistics on terminal, disk and CPU operations.  By default, iostat displays one line of statistics averaged over
     the machine's run time.  The use of -c presents successive lines averaged over the wait period.  The -I option causes iostat to print raw,
     unaveraged values.

     Only the last disk option specified (-d, -D, or -x) is used.

     The options are as follows:

     -c count	 Repeat the display count times.  Unless the -I flag is in effect, the first display is for the time since a reboot and each sub-
		 sequent report is for the time period since the last display.	If no wait interval is specified, the default is 1 second.

     -C 	 Show CPU statistics.  This is enabled by default unless the -d, -D, -T, or -x flags are used.

     -d 	 Show disk statistics.	This is the default.  Displays kilobytes per transfer, number of transfers, and megabytes transferred.
		 Use of this flag disables display of CPU and tty statistics.

     -D 	 Show alternative disk statistics.  Displays kilobytes transferred, number of transfers, and time spent in transfers.  Use of this
		 flag disables the default display.

     -I 	 Show the running total values, rather than an average.

     -M core	 Extract values associated with the name list from the specified core instead of the default ``/dev/mem''.

     -N system	 Extract the name list from the specified system instead of the default ``/netbsd''.

     -T 	 Show tty statistics.  This is enabled by default unless the -C, -d, or -D flags are used.

     -w wait	 Pause wait seconds between each display.  If no repeat count is specified, the default is infinity.

     -x 	 Show extended disk statistics.  Each disk is displayed on a line of its own with all available statistics.  This option overrides
		 all other display options, and all disks are displayed unless specific disks are provided as arguments.  Additionally, separate
		 read and write statistics are displayed.

     iostat displays its information in the following format:

     tty
	   tin	   characters read from terminals
	   tout    characters written to terminals

     disks
	   Disk operations.  The header of the field is the disk name and unit number.	If more than four disk drives are configured in the sys-
	   tem, iostat displays only the first four drives.  To force iostat to display specific drives, their names may be supplied on the com-
	   mand line.

	   KB/t    Kilobytes transferred per disk transfer
	   t/s	   transfers per second
	   MB/s    Megabytes transferred per second

	   The alternative display format, (selected with -D), presents the following values.
	   KB	   Kilobytes transferred
	   xfr	   Disk transfers
	   time    Seconds spent in disk activity

     cpu
	   us	   % of CPU time in user mode
	   ni	   % of CPU time in user mode running niced processes
	   sy	   % of CPU time in system mode
	   id	   % of CPU time in idle mode

FILES

     /netbsd   Default kernel namelist.
     /dev/mem  Default memory file.

SEE ALSO

     fstat(1), netstat(1), nfsstat(1), ps(1), systat(1), vmstat(1), pstat(8)

     The sections starting with ``Interpreting system activity'' in Installing and Operating 4.3BSD.

HISTORY

     iostat appeared in Version 6 AT&T UNIX.  The -x option was added in NetBSD 1.4.

BSD
								   March 1, 2003							       BSD
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