Kstat

- Perl tied hash interface to the kstat facility

Synopsis

use Sun::Solaris::Kstat;

Sun::Solaris::Kstat->new();
Sun::Solaris::Kstat->update();
Sun::Solaris::Kstat->{module}{instance}{name}{statistic}

Description

Kernel statistics are categorized using a 3-part key consisting of the module, the instance, and the statistic name. For example, CPU information can be found under cpu_stat:0:cpu_stat0, as in the above example. The method Sun::Solaris::Kstat→new() creates a new 3-layer tree of Perl hashes with the same structure; that is, the statistic for CPU 0 can be accessed as $ks→{cpu_stat}{0}{cpu_stat0}. The fourth and lowest layer is a tied hash used to hold the individual statistics values for a particular system resource.

For performance reasons, the creation of a Sun::Solaris::Kstat object is not accompanied by a following read of all possible statistics. Instead, the 3-layer structure described above is created, but reads of a statistic's values are done only when referenced. For example, accessing $ks→{cpu_stat}{0}{cpu_stat0}{syscall} will read in all the statistics for CPU 0, including user, system, and wait times, and the other CPU statistics, as well as the number of system call entries. Once you have accessed a lowest level statistics value, calling $ks→update() will automatically update all the individual values of any statistics you have accessed.

There are two values of the lowest-level hash that can be read without causing the full set of statistics to be read from the kernel. These are “class”, which is the kstat class of the statistics, and “crtime”n, which is the time that the kstat was created. See kstat(3KSTAT) for full details of these fields.

Methods

new()

Create a new kstat statistics hierarchy and return a reference to the top-level hash. Use it like any normal hash to access the statistics.

update()

Update all the statistics that have been accessed so far. In scalar context, update() returns 1 if the kstat structure has changed, and 0 otherwise. In list context, update() returns references to two arrays: the first holds the keys of any kstats that have been added, and the second holds the keys of any kstats that have been deleted. Each key will be returned in the form “module:instance:name”.

Examples

Example 1 Sun::Solaris::Kstat example

use Sun::Solaris::Kstat;

my $kstat = Sun::Solaris::Kstat->new();
my ($usr1, $sys1, $wio1, $idle1) =
   @{$kstat->{cpu_stat}{0}{cpu_stat0}}{qw(user kernel 
        wait idle)};
print("usr sys wio idle\n");
while (1) {
   sleep 5;
   if ($kstat->update()) {
           print("Configuration changed\n");
   }
   my ($usr2, $sys2, $wio2, $idle2) =
       @{$kstat->{cpu_stat}{0}{cpu_stat0}}{qw(user kernel 
            wait idle)};
   printf(" %.2d  %.2d  %.2d  %.2d\n",
        ($usr2 - $usr1) / 5, ($sys2 - $sys1) / 5,
        ($wio2 - $wio1) / 5, ($idle2 - $idle1) / 5);
   $usr1 = $usr2;
   $sys1 = $sys2;
   $wio1 = $wio2;
   $idle1 = $idle2;
}

See Also

perl(1), kstat(1M), kstat(3KSTAT), kstat_chain_update(3KSTAT), kstat_close(3KSTAT), kstat_open(3KSTAT), kstat_read(3KSTAT)

Notes

As the statistics are stored in a tied hash, taking additional references of members of the hash, such as

my $ref = \ks->{cpu_stat}{0}{cpu_stat0}{syscall};
print("$$ref\n");

will be recorded as a hold on that statistic's value, preventing it from being updated by refresh(). Copy the values explicitly if persistence is necessary.

Several of the statistics provided by the kstat facility are stored as 64-bit integer values. Perl 5 does not yet internally support 64-bit integers, so these values are approximated in this module. There are two classes of 64-bit value to be dealt with:

64-bit intervals and times

These are the crtime and snaptime fields of all the statistics hashes, and the wtime, wlentime, wlastupdate, rtime, rlentime and rlastupdate fields of the kstat I/O statistics structures. These are measured by the kstat facility in nanoseconds, meaning that a 32-bit value would represent approximately 4 seconds. The alternative is to store the values as floating-point numbers, which offer approximately 53 bits of precision on present hardware. 64-bit intervals and timers as floating point values expressed in seconds, meaning that time-related kstats are being rounded to approximately microsecond resolution.

64-bit counters

It is not useful to store these values as 32-bit values. As noted above, floating-point values offer 53 bits of precision. Accordingly, all 64-bit counters are stored as floating-point values.