Managing Process Class Information

The listing below shows which classes are configured on your system, and the user priority range for the timesharing class. The possible classes are:

• System (SYS)

• Interactive (IA)

• Real-time (RT)

• Timesharing (TS)

  • The user-supplied priority ranges from -20 to +20.

  • The priority of a process is inherited from the parent process. This is referred to as the user-mode priority.

  • The system looks up the user-mode priority in the timesharing dispatch parameter table and adds in any nice or priocntl (user-supplied) priority and ensures a 0-59 range to create a global priority.

Changing the Scheduling Priority of Processes With priocntl

The scheduling priority of a process is the priority it is assigned by the process scheduler, according to scheduling policies. The dispadmin command lists the default scheduling policies. See "Scheduler Configuration", for information on the dispadmin command.

The priocntl command can be used to assign processes to a priority class and to manage process priorities. See the section called "How to Designate a Process Priority" for instructions on using the priocntl command to manage processes.

How to Display Basic Information About Process Classes

You can display process class and scheduling parameters with the priocntl -l command.

$ priocntl -l

Example--Getting Basic Information About Process Classes

The following example shows output from the priocntl -l command.

$ priocntl -l
CONFIGURED CLASSES
==================
 
SYS (System Class)
 
TS (Time Sharing)
	Configured TS User Priority Range: -20 through 20
 

How to Display the Global Priority of a Process

You can display the global priority of a process by using the ps command.

$ ps -ecl

The global priority is listed under the PRI column.

Example--Displaying the Global Priority of a Process

The following example shows output from ps -ecl. Data in the PRI column show that pageout has the highest priority, while sh has the lowest.

$ ps -ecl
 F S UID PID  PPID CLS PRI  ADDR      SZ  WCHAN    TTY      TIME   COMD
19 T 0   0    0    SYS 96   f00d05a8   0           ?        0:03  sched
 8 S 0   1    0    TS  50   ff0f4678 185  ff0f4848 ?       36:51   init
19 S 0   2    0    SYS 98   ff0f4018   0  f00c645c ?        0:01 pageout
19 S 0   3    0    SYS 60   ff0f5998   0  f00d0c68 ?      241:01 fsflush
 8 S 0   269  1    TS  58   ff0f5338 303  ff49837e ?        0:07    sac
 8 S 0   204  1    TS  43   ff2f6008  50  ff2f606e console  0:02     sh
 

How to Designate a Process Priority

1. Become superuser.

2. Start a process with a designated priority.

   # priocntl -e -c class-muserlimit-p pri command_name

   -e	Executes the command.
   -c class	Specifies the class within which to run the process. The default classes are TS (timesharing) or RT (real-time).
   -m userlimit	Specifies the maximum amount you can raise or lower your priority, when using the -p option.
   -p pri command_name	Lets you specify the relative priority in the RT class, for a real-time thread. For a timesharing process, the -p option lets you specify the user-supplied priority which ranges from -20 to +20.

3. Verify the process status by using the ps -ecl command.

   # ps -ecl | grep command_name

Example--Designating a Priority

The following example starts the find command with the highest possible user-supplied priority.

# priocntl -e -c TS -m 20 -p 20 find . -name core -print

# ps -ecl | grep find

How to Change Scheduling Parameters of a Timeshare Process

1. Become superuser.

2. Change the scheduling parameter of a running timeshare process.

   # priocntl -s -m userlimit [-p userpriority] -i idtype idlist

   -s	Lets you set the upper limit on the user priority range and change the current priority.
   -m userlimit	Specifies the maximum amount you can raise or lower your priority, when using the -p option.
   -p userpriority	Allows you to designate a priority.
   -i idtype idlist	Uses a combination of idtype and idlist to identify the process. The idtype specifies the type of ID, such as PID or UID.

3. Verify the process status by using the ps --ecl command.

   # ps -ecl | grep idlist

Example--Changing Scheduling Parameters of a Timeshare Process

The following example executes a command with a 500-millisecond time slice, a priority of 20 in the RT class, and a global priority of 120.

# priocntl -e -c RT -t 500 -p 20 myprog
# ps -ecl | grep myprog

How to Change the Class of a Process

1. (Optional) Become superuser.

   ---

   Note -

   You must be superuser or working in a real-time shell to change processes from, or to, real-time processes.

   ---

2. Change the class of a process.

   # priocntl -s -c class -i idtype idlist

   -s	Lets you set the upper limit on the user priority range and change the current priority.
   -c class	Specifies the class, TS or RT, to which you are changing the process.
   -i idtype idlist	Uses a combination of idtype and idlist to identify the process. The idtype specifies the type of ID, such as PID or UID.

3. Verify the process status by using the ps -ecl command.

   # ps -ecl | grep idlist

Example--Changing the Class of a Process

The following example changes all the processes belonging to user 15249 to real-time processes.

# priocntl -s -c RT -i uid 15249
# ps -ecl | grep 15249

If, as superuser, you change a user process to the real-time class, the user cannot subsequently change the real-time scheduling parameters (using priocntl -s).

Changing the Priority of a Timesharing Process With nice

The nice command is only supported for backward compatibility to previous Solaris releases. The priocntl command provides more flexibility in managing processes.

The priority of a process is determined by the policies of its scheduling class, and by its nice number. Each timesharing process has a global priority which is calculated by adding the user-supplied priority, which can be influenced by the nice or priocntl commands, and the system-calculated priority.

The execution priority number of a process is assigned by the operating system, and is determined by several factors, including its schedule class, how much CPU time it has used, and (in the case of a timesharing process) its nice number.

Each timesharing process starts with a default nice number, which it inherits from its parent process. The nice number is shown in the NI column of the ps report.

A user can lower the priority of a process by increasing its user-supplied priority. But only the superuser can lower a nice number to increase the priority of a process. This is to prevent users from increasing the priorities of their own processes, thereby monopolizing a greater share of the CPU.

Nice numbers range between 0 and +40, with 0 representing the highest priority. The default value is 20. Two versions of the command are available, the standard version, /usr/bin/nice, and a version that is part of the C shell.

How to Change the Priority of a Process

You can raise or lower the priority of a command or a process by changing the nice number. To lower the priority of a process:

The first and second commands increase the nice number by four units (the default); and the third command increases the nice by ten units, lowering the priority of the process.

The following commands raise the priority of the command by lowering the nice number.

To raise the priority of a process:

The above commands raise the priority of the command, command_name, by lowering the nice number. Note that in the second case, the two minus signs are required.

Process Troubleshooting

Here are some tips on obvious problems you may find:

• Look for several identical jobs owned by the same user. This may come as a result of running a script that starts a lot of background jobs without waiting for any of the jobs to finish.

• Look for a process that has accumulated a large amount of CPU time. You'll see this by looking at the TIME field. Possibly, the process is in an endless loop.

• Look for a process running with a priority that is too high. Type ps -c to see the CLS field, which displays the scheduler class of each process. A process executing as a real-time (RT) process can monopolize the CPU. Or look for a timeshare (TS) process with a high nice value. A user with superuser privileges may have bumped up the priorities of this process. The system administrator can lower the priority by using the nice command.

• Look for a runaway process--one that progressively uses more and more CPU time. You can see it happening by looking at the time when the process started (STIME) and by watching the cumulation of CPU time (TIME) for awhile.