The following is a demonstration of the priclass.d script.


The script was run for several seconds then Ctrl-C was hit. During
this time, other processes in different scheduling classes were
running.

   # ./priclass.d
   Sampling... Hit Ctrl-C to end.
   ^C
   
     IA
              value  ------------- Distribution ------------- count
                 40 |                                         0
                 50 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 30
                 60 |                                         0
   
     SYS
              value  ------------- Distribution ------------- count
                < 0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@  4959
                  0 |                                         0
                 10 |                                         0
                 20 |                                         0
                 30 |                                         0
                 40 |                                         0
                 50 |                                         0
                 60 |                                         30
                 70 |                                         0
                 80 |                                         0
                 90 |                                         0
                100 |                                         0
                110 |                                         0
                120 |                                         0
                130 |                                         0
                140 |                                         0
                150 |                                         0
                160 |                                         50
             >= 170 |                                         0
   
     RT
              value  ------------- Distribution ------------- count
                 90 |                                         0
                100 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 110
                110 |                                         0
   
     TS
              value  ------------- Distribution ------------- count
                < 0 |                                         0
                  0 |@@@@@@@@@@@@@@@                          2880
                 10 |@@@@@@@                                  1280
                 20 |@@@@@                                    990
                 30 |@@@@@                                    920
                 40 |@@@@                                     670
                 50 |@@@@                                     730
                 60 |                                         0

The output is quite interesting, and illustrates neatly the behaviour
of different scheduling classes.

The IA interactive class had 30 samples of a 50 to 59 priority, a fairly
high priority. This class is used for interactive processes, such as
the windowing system. I had clicked on a few windows to create this
activity.

The SYS system class has had 4959 samples at a < 0 priority - the lowest,
which was for the idle thread. There are a few samples at higher
priorities, including some in the 160 to 169 range (the highest), which
are for interrupt threads. The system class is used by the kernel.

The RT real time class had 110 samples in the 100 to 109 priority range.
This class is designed for real-time applications, those that must have
a consistant response time regardless of other process activity. For that
reason, the RT class trumps both TS and IA. I created these events by
running "prstat -R" as root, which runs prstat in the real time class.

The TS time sharing class is the default scheduling class for the processes
on a Solaris system. I ran an infinite shell loop to create heavy activity,
"while :; do :; done", which shows a profile that leans towards lower
priorities. This is deliberate behaivour from the time sharing class, which
reduces the priority of CPU bound processes so that they interefere less
with I/O bound processes. The result is more samples in the lower priority
ranges.